cogl: Pull in the code for GLU tesselator from Mesa/SGI

cogl: Pull in the code for GLU tesselator from Mesa/SGI

This copies the files for the GLU tesselator from Mesa. The Mesa code
is based on the original SGI code and is released under a BSD license.

The memalloc.h header has been replaced with one that forces the code
to use g_malloc and friends. The rest of the files are not altered
from the original so it should be possible to later upgrade the files
by simply overwriting them.

There is a tesselator.h header which is expected to be included by
rest of Cogl to use the tesselator. This contains a trimmed down
version of glu.h that only includes parts that pertain to the
tesselator. There is also a stub glu.h in the GL directory which is
just provided so that the tesselator code can include <GL/gl.h>
without depending on the system header. It just redirects to
tesselator.h