Merge tag 'v0.31.0' into debian

Alpha 31 release
Use persistent buffer mapping for dynamic buffer objects.
Merge branch 'master' into vertexpack
Allow disabling of buffer object extensions

This is useful for testing purposes since these extensions are currently optional
Fix NULL dereference crash
Only drop the mouseup without mousedown event if the key is mouse1
Remove USE_DEFORM_VERTEXES macro.
Remove USE_EYE_OUTSIDE macro.
Merge branch 'master' into vertexpack

Conflicts:
	src/engine/renderer/tr_vbo.cpp
Add cvar to disable GL_ARB_sync.
Fix building on old GLEW.
Fix inverted if condition.

This caused the engine to allocate a too small VBO and thus resulted
in low FPS or even crashed the game.
Remove useless extern "C"
Add a check to avoid sending sync messages while handling async messages
Remove USE_FRUSTUM_CULLING macro.
Remove BRIGHTPASS_FILTER macro.
Remove USE_GBUFFER macro.
Refactor vertex deformation code.
Consistent alien buy menu colors.
Consistent human buy menu colors.