configure: s/libpoppler/libpoppler-glib/

To be precise, we require the libpoppler-glib, which is optional when
building poppler. It is more informative to be accurate.
Fix make distcheck.

Use srcdir/abs_srcdir in Makefile.am for dealing with VPATH builds.
Bug 706275 - "View/Snap to active path" doesn't snap to layer center...

...with the Move tool

Add the missing code to snap to the rectangle's center in
gimp_image_snap_rectangle().
plug-ins, pdb: Add missing break statements to switch in correct file
Prevent possible crash when loading file with scheme_load_file.
From SVN version 101 of offical version of TinyScheme.
Don't need to use snprintf() in atom2str to return some fixed strings.
From SVN version 102 of offical version of TinyScheme.
build/win: Upgrade librsvg to 2.40.2
app: g_file_new_for_uri() return object not freed with g_object_unref().

Non-freed GFile object when saving or exporting the first time, i.e.
with default extensions.
app: set win32 only code between #ifdef G_OS_WIN32

PATHEXT environment variable to determine whether a file is executable
or not is a Windows-only concept.
configure: fix testing for bzip2 on windows
app: interpreter arguments for plugins not returned.

When a plugin file's shebang would start with "/usr/bin/env", the
interpreter's arguments were not returned by resolve_sh_bang().
Makefile.am: Add gtk-doc.make to EXTRA_DIST
Bug 732072: Image windows created by script-fu plug-ins...

are opened behind the previously focused Image Window

libgimp/gimpui.c bypasses gtk in setting the transient_for
property and so it is not possible to call
gtk_set_transient_for (dialog, NULL), but it is necessary
to go directly to the gdk level.
build: Update configure help
Updated Russian translation:

 * Fixed https://bugzilla.gnome.org/show_bug.cgi?id=674076
app: Use gint64 for dirty_time
devel-docs: Add libtool-instructions.txt
INSTALL: update gexiv2 URL and remove a repetitive sentence.
devel-docs: add some info about libtool versioning to release-howto.txt
app: don't try to draw a NULL boundary in gimp_region_select_tool_draw()