refactor to allow various gfx backends (work-in-progress)
enable OpenGL3 by default (part of work-in-progress refactor)
fix max osx build
add alpha blendering option (disabled by default) using w component of color
add low-level support function demo (test)
fix build error in SupportFuncDemo.h
add support to btHingeConstraint to set/get ERP, example use:
hinge->setParam(BT_CONSTRAINT_ERP,0.5);
btScalar erp = hinge->getParam(BT_CONSTRAINT_ERP);
Also, preliminary support for status bar messages in demo framework.
fix double precision build
Merge pull request #271 from erwincoumans/master

 btHingeConstraint to set/get ERP, refactor gfx backends (work-in-progress)