Refresh GLEW with DSA workaround - ignore fp64 stuff.
Add Mesa3D to the lists of known OpenGL implementations for Linux GLX.
For GLUT on Windows, simple ASCII to UCS2 unicode conversion for SetWindowText.
For DSA emulation layer, use Regal::DispatchTable::call rather than calling back into the emulation layer directly.  For github issue #65.

https://github.com/p3/regal/issues/65
Initial multi-threading for global context mappings
Initial implementation of Iff::Cleanup for claiming back GL resources, if possible.
Merge remote-tracking branch 'github/master' into cass
proposed fix for issue #68 reported by jra101