Bug#836426: Caused by libgtk-3-0 3.21

[Josh Triplett]

Control: reassign -1 libgtk-3-0 3.21.5-3
Control: affects -1 gnome-boxes
Control: severity -1 serious
Control: forcemerge -1 832077
Control: affects 832077 emacs24

I downgraded libgtk-3-0 to 3.20.9-1, and that fixed this bug.

Running gnome-boxes with libgtk-3-0 3.21.5-3 and running a VM with
display via Spice triggers this issue.  Looking at the console shows
numerous error messages about GtkGrid and GtkOverlay objects "drawn
without a current allocation", starting at the point when rendering
stops working.  That doesn't occur with libgtk-3-0 3.20.9-1.

Searching turns up various other mentions of applications breaking with
similar error messages when using GTK+ 3.21.  I've merged this bug with
another libgtk-3-0 bug reporting a similar issue with emacs24, and
raised the severity as it affects other packages as well; this looks
like a widespread issue.

- Josh Triplett