quartz: fix build on 10.6 and below

It is not possible to successfully build GTK+ on OS X 10.6 and below
since NSFullScreenWindowMask is only available starting with 10.7. Add
ifdef guards around setStyleMask: in order to allow it to build on
earlier OS X releases.

https://bugzilla.gnome.org/show_bug.cgi?id=737561
quartz: Move the FullscreenSavedGeometry definition earlier

Move the FullscreenSavedGeometry before the first (conditional)
use, to fix the build on OS X 10.6.

https://bugzilla.gnome.org/show_bug.cgi?id=737561
testlevelbar: don't segfault when quitting testlevelbar

Quit the mainloop when the window is closed.

https://bugzilla.gnome.org/show_bug.cgi?id=707695
levelbar: don't use the current value style class for empty blocks

We want to be able to style the empty blocks independently of all the
offset styles, so remove the current style class when painting an empty
block.

https://bugzilla.gnome.org/show_bug.cgi?id=707695
testlevelbar: fix CSS to be aligned with documentation

https://bugzilla.gnome.org/show_bug.cgi?id=707695
Ignore gdk-pixbuf deprecations
popover menus: Take iconic into account

We don't want separators in both side of an iconic section
and use a 10px margin to separate two iconic sections.

Separators are also updated in case of dynamic insertion
( often used with menu items for plugins )

https://bugzilla.gnome.org/show_bug.cgi?id=738650
Indentation fix