[warningectomy] remove unused variable
dox: Fix typo
[cleanup] Remove unused pretty_format_xml option
Bug 710818 - Overflow safe wrappers for acos/asin

acos() and asin() are only defined in a certain range. Implement some
range/overflow safe wrappers rather than potentially passing infinite
to other modules (e.g. cairo did assert() on it.)
Obsolete color_gdk_black, color_gdk_white global variables

These variables need system/compiler specific handling and are
considered bad programming style anyway. This is also fixing
some theming issue with the line width widget, instead of
unconditional black now using the widgets foreground color.
Initialize render_bounding_boxes from environment variable

Remove one more global variable using DIAVAR, setting this from
.dia/persistence wasn't that convenient anyway.
Fix Beziergon behavior after restructuring

Adding and removing points (segments) to the Beziergon did not work as
before due to changes from 62dab7da68. Actually that commit did not take
into account, that bezierconn_closest_segment() returned 0 for the first
segment but beziershape_closest_segment() returned 1.
Now the segment index is zero-based as expected and the Beziergon code
use the appropriate offsets to deal with it.
Also a unit-test is specifically written for Add/Remove Segment to not
introduce such bugs with upcoming restructuring.
[unit test] Extend Add/Delete point test to "poly_points"

Polygons and Polylines should behave similar to Beziergon and
Bezierline regarding adding/removing of points/segments.
The assumption does not hold for "orth_points", though.
[clang-cl] Improved DIAVAR handling

While compiling Dia with clang-cl [1] there was a problem with multiple
definitions of variables declared with DIAVAR. Apparently the MS compiler
is more forgiving with inclusion of '__declspec(dllexport) Type name;'
in multiple translation units. clang-cl was producing colliding symbols
in different obj files. The implemented fix is treating DIAVAR and the
extern keyword as orthogonal concepts. So for a global variable the
declaration is 'extern DIAVAR SomeType name;' while the instantiation
is just 'DIAVAR SomeType name;'.
This also fixes a gcc complaint about an external variable being
initialized (in units.c).
Of course the best way to handle global variables is to get rid of them
altogether.

[1] http://blog.llvm.org/2013/11/the-clang-cl-fallback-mode.html
[clang-cl] Avoid l-value cast for everything but msvc

clang-cl did not like that pattern as well even in compatibility mode
Bug 711418 - Handle diagram file with comments

A comment as the first part in the XML file was prohibiting to load
the file at all with “Not a Dia file” error.