Update uniforms after glColor().

The updates were not propagated because Iff::UpdateUniforms()
did not think that there was a change.
Extend emulation dispatch to hinting.
GLEW refresh (w.r.t opengl.org)
Some GL API harmonization with apitrace.
Add Regal support for GL_SGIX_ycrcb
Further GL_REGAL_enable support for glEnable/glDisable of dispatch layers.
DSA emulation moved to downstream of Regal::Emu::Iff
Trace dispatch fixes for WGL
Support for REGAL_TRACE_FILE setting, and JSON property.
Tidy-up of Regal::Emu::Filt