moglcore: Add immediate mode emulation for OpenGL-ES.

Integrate ftglesGlue.h/.cpp from David Petrie and hook it up
to some new moglcore function which emulate missing immediate
mode counterparts on top of client vertex arrays and batch
submission: glBegin -> ftglBegin, glEnd -> ftglEnd, ...

Emulated are glBegin, glEnd, glColor4f, glTexCoord2f, glVertex3f
and glVertex4f. Other immediate mode functions stay unavailable,
but this is the bare minimum to allow use of code written against
desktop OpenGL1/2 immediate mode under OpenGL-ES.

The MOGL wrappers have conditional execution of the glXXX or ftglXXX
variants, depending IfGLES() or not.

-> moglcore for 64-Bit Octave on Linux rebuilt and tested.
-> ShepardZoomDemo slightly modified to make it work this way.
-> Test on Nexus pending.

There may be a bug in GLEW which causes glGetPointerv() to be
defined to a NULL pointer, causing a crash if used! Worked around
in this emulation code by #undef glGetPointerv to get the native
entry point instead of GLEW's broken/dysfunctional #define override.
-> This needs further investigation.