Implement glPopAttrib(GL_TRANFORM_BIT)

Extend the existing RegalPPa/RegalState functionality to add support for
saving and restoring the server side transform state.

Unlike the other emulated functionlity in RegalState, the code I added
does minimize the state transitions, which is especially a good idea if
the backend does not support certain state (such as clip planes) that
may not be actually set by the Regal client.

Extends the testRegalState test to fully cover the new state code. Adds
a quick test for the PushAttrib/PopAttrib calls.

Half of the fix for Regal Issue #27.
Merge branch 'implement_ppa_transform_bit' of git://github.com/adhoc-bobcat/regal
Rename Regal::RegalPpa -> Regal::Emu:Ppa
use std::swap_ranges for swapping arrays.
Make the dispatch table initializers available to regaltest.
White-list more GL functions into RegalDispatchGMock, for regaltest purposes.
freeglut tidy-up for possible upstreaming.
For X11/EGL mode, include additional X11 headers that would have come from GL/EGL.h