Revert "remove useless manual lock recursion check in gl mutex"

It was actually useful to know when to release the glcontext.
Merge branch 'master' into jitv

Conflicts:
	engine/rendergl.cpp
Do not try to halt the gfx if vsync == 0
respect menufps, force vsync 1 in mainmenu, do not run unbounded if minimized
if vsync == 0 and in game, busy poll for new jobs in the drawer thread