Rather evil crasher in 3.6.3

[Benjamin Otte <otte gnome org>]

Hi,

Apparently GTK 3.6.3 contains a small bugfix that causes a rather
severe crasher. It happens at least whenever you try to measure the
size of a combobox, but there's probably other callers of
gtk_style_context_get_font() that fall into this particular trap. And
because a lot of applications use GtkComboBox, a lot of applications
are now instantly crashing.

The bug reference is
  https://bugzilla.gnome.org/show_bug.cgi?id=691186
and the fix can be found attached there and committed to the gtk-3-6 branch as
  http://git.gnome.org/browse/gtk+/commit/?h=gtk-3-6&id=7f0b30d7d40acaaaa2ecda603903c00544232bb8

I haven't talked to Matthias about it, but I think we want to do a
quick 3.6.4 release to fix this. Distributions that have already
upgraded to 3.6.3 want to quickly apply the patch, others should
probably skip 3.6.3 and wait for 3.6.4.

Fwiw, the testsuite should have caught this particular bug -
tests/reftests/inherit-and-initial.ui was SEGVing - but that must have
slipped through the cracks somehow. We should make sure that if we do
builds and tests, we also do them for git stable, because that branch
seems to be very rarely run before it's released, so messups like
these don't get noticed.

Benjamin