PsychtoolboxPostInstallRoutine: Further instructions for Nexus-7 setup.

Don't forget the LD_PRELOAD workaround needed due to the fact that
octave in 13.04 Raring for ARM/Nexus-7 is built with a hard dependency
on libGL.so, the desktop OpenGL library. We need this library, but
the OpenGL-ES1 lib must take precedence in linking of symbols, otherwise
we'd link against dead functions from a zombie GL lib and would crash
pretty quickly!

Todo: Report octave bug upstream.

This should finalize initial bringup for OpenGL-ES1 / ARM / Nexus-7.
More detail work will follow, but that can happen in the mainstream
development branch. The wafflegles branch should be ready for merge,
assuming no regressions were introduced for other operating systems.