Import Valgrind suppression rules from GNOME.supp.

Built from:
https://github.com/dtrebbien/GNOME.supp
d12f8759856462e0b92596a33ceb82878266403f
Add script to run HoverRace w/ Valgrind.
Use custom Valgrind suppressions.
Don't cache wide string on Linux.

The wide string is only cached for the Win32 text rendering; the Pango
text rendering only uses the UTF-8 string.
Use C++ initialization list.

This also initializes mZBuffer (detected by Valgrind).