[gtk-osx] fallback font context for running console version

this is needed to successfully run the unit test on OS X
[unit test] _test_draw() exceptions for osx/x64

Calculation results in extreme cases are slightly of between platforms,
not sure if it is the C-runtime or compiler differences.
[warningectomy] implicit conversion from enumeration type DiaSvgLineDefaults

Actually a design change: formerly we were relying on weak typing of enums,
i.e. assigning values from the wrong enum to e.g. to type 'LineJoin'. Now
*_DEFAULT variants are part of the main enum, e.g LineJoin and has to be
handled explicitely on the consumer level, here mostly renderers.

Removes the following warnings:

dia_svg.c:71:56: warning: implicit conversion from enumeration type 'enum DiaSvgLineDefaults' to different enumeration type 'LineCaps' [-Wenum-conversion]
  gs->linecap = parent_style ? parent_style->linecap : DIA_SVG_LINECAPS_DEFAULT;
              ~                                        ^~~~~~~~~~~~~~~~~~~~~~~~
dia_svg.c:72:58: warning: implicit conversion from enumeration type 'enum DiaSvgLineDefaults' to different enumeration type 'LineJoin' [-Wenum-conversion]
  gs->linejoin = parent_style ? parent_style->linejoin : DIA_SVG_LINEJOIN_DEFAULT;
               ~                                         ^~~~~~~~~~~~~~~~~~~~~~~~
dia_svg.c:73:60: warning: implicit conversion from enumeration type 'enum DiaSvgLineDefaults' to different enumeration type 'LineStyle' [-Wenum-conversion]
  gs->linestyle = parent_style ? parent_style->linestyle : DIA_SVG_LINESTYLE_DEFAULT;
                ~                                          ^~~~~~~~~~~~~~~~~~~~~~~~~
dia_svg.c:484:19: warning: implicit conversion from enumeration type 'enum DiaSvgLineDefaults' to different enumeration type 'LineJoin' [-Wenum-conversion]
    s->linejoin = DIA_SVG_LINEJOIN_DEFAULT;
                ~ ^~~~~~~~~~~~~~~~~~~~~~~~
dia_svg.c:496:18: warning: implicit conversion from enumeration type 'enum DiaSvgLineDefaults' to different enumeration type 'LineCaps' [-Wenum-conversion]
    s->linecap = DIA_SVG_LINECAPS_DEFAULT;
               ~ ^~~~~~~~~~~~~~~~~~~~~~~~
dia_svg.c:694:17: warning: implicit conversion from enumeration type 'enum DiaSvgLineDefaults' to different enumeration type 'LineStyle' [-Wenum-conversion]
        s->linestyle = DIA_SVG_LINESTYLE_DEFAULT;
                     ~ ^~~~~~~~~~~~~~~~~~~~~~~~~
shape_info.c:121:32: warning: comparison of constant -1 with expression of type 'Alignment' is always false [-Wtautological-constant-out-of-range-compare]
      if (el->text.s.alignment == -1)
          ~~~~~~~~~~~~~~~~~~~~ ^  ~~
shape_info.c:911:2: warning: implicit conversion from enumeration type 'enum DiaSvgLineDefaults' to different enumeration type 'LineCaps' [-Wenum-conversion]
        DIA_SVG_LINECAPS_DEFAULT, DIA_SVG_LINEJOIN_DEFAULT, DIA_SVG_LINESTYLE_DEFAULT, 1.0
        ^~~~~~~~~~~~~~~~~~~~~~~~
shape_info.c:911:28: warning: implicit conversion from enumeration type 'enum DiaSvgLineDefaults' to different enumeration type 'LineJoin' [-Wenum-conversion]
        DIA_SVG_LINECAPS_DEFAULT, DIA_SVG_LINEJOIN_DEFAULT, DIA_SVG_LINESTYLE_DEFAULT, 1.0
                                  ^~~~~~~~~~~~~~~~~~~~~~~~
shape_info.c:911:54: warning: implicit conversion from enumeration type 'enum DiaSvgLineDefaults' to different enumeration type 'LineStyle' [-Wenum-conversion]
        DIA_SVG_LINECAPS_DEFAULT, DIA_SVG_LINEJOIN_DEFAULT, DIA_SVG_LINESTYLE_DEFAULT, 1.0
                                                            ^~~~~~~~~~~~~~~~~~~~~~~~~
custom_object.c:926:26: warning: comparison of constant 'DIA_SVG_LINECAPS_DEFAULT' (20) with expression of type 'LineCaps' is always false [-Wtautological-constant-out-of-range-compare]
  if ((el->any.s.linecap == DIA_SVG_LINECAPS_DEFAULT && (*cur_caps) != LINECAPS_BUTT) ||
       ~~~~~~~~~~~~~~~~~ ^  ~~~~~~~~~~~~~~~~~~~~~~~~
custom_object.c:928:39: warning: comparison of constant 'DIA_SVG_LINECAPS_DEFAULT' (20) with expression of type 'LineCaps' is always true [-Wtautological-constant-out-of-range-compare]
      (*cur_caps) = (el->any.s.linecap!=DIA_SVG_LINECAPS_DEFAULT) ?
                     ~~~~~~~~~~~~~~~~~^ ~~~~~~~~~~~~~~~~~~~~~~~~
custom_object.c:932:26: warning: comparison of constant 'DIA_SVG_LINEJOIN_DEFAULT' (20) with expression of type 'LineJoin' is always false [-Wtautological-constant-out-of-range-compare]
  if ((el->any.s.linejoin==DIA_SVG_LINEJOIN_DEFAULT && (*cur_join)!=LINEJOIN_MITER) ||
       ~~~~~~~~~~~~~~~~~~^ ~~~~~~~~~~~~~~~~~~~~~~~~
custom_object.c:934:38: warning: comparison of constant 'DIA_SVG_LINEJOIN_DEFAULT' (20) with expression of type 'LineJoin' is always true [-Wtautological-constant-out-of-range-compare]
    (*cur_join) = (el->any.s.linejoin!=DIA_SVG_LINEJOIN_DEFAULT) ?
                   ~~~~~~~~~~~~~~~~~~^ ~~~~~~~~~~~~~~~~~~~~~~~~
custom_object.c:938:28: warning: comparison of constant 'DIA_SVG_LINESTYLE_DEFAULT' (20) with expression of type 'LineStyle' is always false [-Wtautological-constant-out-of-range-compare]
  if ((el->any.s.linestyle == DIA_SVG_LINESTYLE_DEFAULT &&
       ~~~~~~~~~~~~~~~~~~~ ^  ~~~~~~~~~~~~~~~~~~~~~~~~~
custom_object.c:940:40: warning: comparison of constant 'DIA_SVG_LINESTYLE_DEFAULT' (20) with expression of type 'LineStyle' is always true [-Wtautological-constant-out-of-range-compare]
    (*cur_style) = (el->any.s.linestyle!=DIA_SVG_LINESTYLE_DEFAULT) ?
                    ~~~~~~~~~~~~~~~~~~~^ ~~~~~~~~~~~~~~~~~~~~~~~~~
svg-import.c:468:25: warning: comparison of constant 'DIA_SVG_LINESTYLE_DEFAULT' (20) with expression of type 'LineStyle' is always true [-Wtautological-constant-out-of-range-compare]
      if (gs->linestyle != DIA_SVG_LINESTYLE_DEFAULT)
          ~~~~~~~~~~~~~ ^  ~~~~~~~~~~~~~~~~~~~~~~~~~
svg-import.c:524:24: warning: comparison of constant 'DIA_SVG_LINEJOIN_DEFAULT' (20) with expression of type 'LineJoin' is always true [-Wtautological-constant-out-of-range-compare]
      if (gs->linejoin != DIA_SVG_LINEJOIN_DEFAULT)
          ~~~~~~~~~~~~ ^  ~~~~~~~~~~~~~~~~~~~~~~~~
svg-import.c:530:23: warning: comparison of constant 'DIA_SVG_LINECAPS_DEFAULT' (20) with expression of type 'LineCaps' is always true [-Wtautological-constant-out-of-range-compare]
      if (gs->linecap != DIA_SVG_LINECAPS_DEFAULT)
          ~~~~~~~~~~~ ^  ~~~~~~~~~~~~~~~~~~~~~~~~
[warningectomy] more '%' conversions than data arguments

load_save.c:1136:97: warning: more '%' conversions than data arguments [-Wformat]
    dia_context_add_message_with_errno(ctx, errno, _("Can't rename %s to final output file %s: %s\n"),
                                                                                               ~^
[warningectomy] format string is not a string literal

Now also fix dia_assert_true() declaration and use.

debug.c:39:15: warning: format string is not a string literal [-Wformat-nonliteral]
    g_vprintf(format, args);
              ^~~~~~

And followup warnings of the fix:

object.c:1109:49: warning: more '%' conversions than data arguments [-Wformat]
                    "%s: Object %p has illegal type name %p (%s)\n",
                                                             ~^
object.c:1118:45: warning: format specifies type 'char *' but the argument has
      type 'const DiaObject *' (aka 'const struct _DiaObject *') [-Wformat]
                      "%s: Object %p has null handles\n", obj);
                       ~~                                 ^~~
object.c:1118:22: warning: more '%' conversions than data arguments [-Wformat]
                      "%s: Object %p has null handles\n", obj);
                                  ~^
[warningectomy] unused function 'goal_create_change'

goal.c:482:1: warning: unused function 'goal_create_change' [-Wunused-function]
goal_create_change(Goal *goal, ObjectChange *inner, ConnPointLine *cpl) {
^
[warningectomy] more '%' conversions than data arguments

xfig-import.c:1062:78: warning: more '%' conversions than data arguments [-Wformat]
            dia_context_add_message_with_errno(ctx, errno, _("Couldn't read color: %s\n"));
                                                                                   ~^
[warningectomy] explicitly assigning a variable to itself

vdx-import.c:2997:15: warning: explicitly assigning a variable of type 'const char *' to itself [-Wself-assign]
        for (s=s; *s; s++)
             ~^~
vdx-import.c:3008:15: warning: explicitly assigning a variable of type 'const char *' to itself [-Wself-assign]
        for (s=s; *s; s++)
             ~^~
[warningectomy] unused function 'no_import_pdf'

pdf.c:27:1: warning: unused function 'no_import_pdf' [-Wunused-function]
no_import_pdf(const gchar *filename, DiagramData *dia, DiaContext *ctx, void* user_data)
^
[warningectomy] more format issues with dia_assert_true()

class.c:2433:13: warning: format specifies type 'void *' but the argument has type 'int' [-Wformat]
                  msg, c, i, &c->connections[i],
                          ^
class.c:2434:5: warning: format specifies type 'int' but the argument has type 'ConnectionPoint *' (aka 'struct _ConnectionPoint *') [-Wformat]
                  obj->connections[i + umlclass_num_dynamic_connectionpoints(c)],
                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
class.c:2435:5: warning: data argument not used by format string [-Wformat-extra-args]
                  i + umlclass_num_dynamic_connectionpoints(c));
                  ^
[warningectomy] incompatible pointer types passing 'GObject *' ...

sheets_dialog.c:254:24: warning: incompatible pointer types passing 'GObject *' (aka 'struct _GObject *') to parameter of type 'GtkObject *' (aka 'struct _GtkObject *') [-Wincompatible-pointer-types]
  gtk_object_set_data (G_OBJECT (sheets_shapeselection_dialog), "sheets_shapeselection_dialog", sheets_shapeselection_dialog);
                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/glib-2.0/gobject/gobject.h:51:37: note: expanded from macro 'G_OBJECT'
                                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/gtk-2.0/gtk/gtkobject.h:181:49: note: passing argument to parameter 'object' here
void     gtk_object_set_data         (GtkObject      *object,
                                                      ^
sheets_dialog.c:258:24: warning: incompatible pointer types passing 'GObject *' (aka 'struct _GObject *') to parameter of type 'GtkObject *' (aka 'struct _GtkObject *') [-Wincompatible-pointer-types]
  gtk_object_set_data (G_OBJECT (sheets_shapeselection_dialog), "ok_button", ok_button);
                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/glib-2.0/gobject/gobject.h:51:37: note: expanded from macro 'G_OBJECT'
                                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/gtk-2.0/gtk/gtkobject.h:181:49: note: passing argument to parameter 'object' here
void     gtk_object_set_data         (GtkObject      *object,
                                                      ^
sheets_dialog.c:267:24: warning: incompatible pointer types passing 'GObject *' (aka 'struct _GObject *') to parameter of type 'GtkObject *' (aka 'struct _GtkObject *') [-Wincompatible-pointer-types]
  gtk_object_set_data (G_OBJECT (sheets_shapeselection_dialog), "cancel_button1", cancel_button1);
                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/glib-2.0/gobject/gobject.h:51:37: note: expanded from macro 'G_OBJECT'
                                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/gtk-2.0/gtk/gtkobject.h:181:49: note: passing argument to parameter 'object' here
void     gtk_object_set_data         (GtkObject      *object,
                                                      ^
[warningectomy] incompatible pointer types passing ...

test-boundingbox.c:152:58: warning: incompatible pointer types passing 'void (const struct _TestBeziers *)' to parameter of type 'GTestDataFunc' (aka 'void (*)(gconstpointer)') [-Wincompatible-pointer-types]
      g_test_add_data_func (testpath, &_test_beziers[i], _check_one_bezier);
                                                         ^~~~~~~~~~~~~~~~~
test-svg.c:117:55: warning: incompatible pointer types passing 'void (const PathData *)' to parameter of type 'GTestDataFunc' (aka 'void (*)(gconstpointer)') [-Wincompatible-pointer-types]
      g_test_add_data_func (testpath, &_test_path[i], _check_one_path);
                                                      ^~~~~~~~~~~~~~~
[warningectomy] unused function 'color_to_abgr'

just removed
[warningectomy] unused variable 'bezpointprop_ops'

now the property is registered but still not used
[warningectomy] remove unused variables and functions

the special text editing 'accumulating' was unfinished for too long.
Now it's gone with it's warnings.

textedit.c:148:19: warning: unused variable 'change' [-Wunused-variable]
  TextEditChange *change;
                  ^
textedit.c:370:1: warning: unused function 'text_edit_create_change' [-Wunused-function]
text_edit_create_change(Text *text)
^
textedit.c:394:1: warning: unused function 'text_edit_update' [-Wunused-function]
text_edit_update(TextEditChange *change)
^
[warningectomy] unused function 'draw_text_line' (removed)

render_metapost.c:830:1: warning: unused function 'draw_text_line' [-Wunused-function]
draw_text_line(DiaRenderer *self, TextLine *text_line,
^
[glib-deprecated] g_thread_create() replaced by g_thread_try_new()
[warningectomy] comparison of unsigned enum expression < 0 is always false

cursor.c:76:37: warning: comparison of unsigned enum expression < 0 is always false [-Wtautological-compare]
  if (ctype >= MAX_CURSORS || ctype < 0) {
                              ~~~~~ ^ ~
[warningectomy] no previous prototype for function

sheets.c:419:1: warning: no previous prototype for function 'sheets_dialog_show_callback' [-Wmissing-prototypes]
sheets_dialog_show_callback(GtkAction *action)
^
[warningectomy] no previous prototype for function 'path_combine'

Add one more single function header.