Due to the way Mesa always builds now if a package requires it (i.e. ignoring
system provided libGL), this now causes some problems.

Specifically qt2-libs no longer builds GL support because libGL links against
libpthread on -current and -thread isn't an option we turn on by default on
qt2.

This then breaks sub-packages of qt2-libs which think GL support is in there
(py-qt2 in this case). Just lots of fallout in my bulk builds.

Does anyone know of a reason we shouldn't just enable threads for qt2-libs?
Between pth and system threads, etc I don't think the support is any worse
for it than qt3-libs which we already do multi-threaded there.

(I almost have to done building but then need to do a bulk build with it
to see what packages may break).

James