This is a nearly verbatim copy of the GLU tessellator source code from
SGI's OpenGL Sample Implementation at
http://oss.sgi.com/projects/ogl-sample/ . Per
http://oss.sgi.com/projects/FreeB/ , the code is covered under the SGI
Free Software License B, version 2.0, a copy of which is in
LICENSE.txt in this directory.

The following changes were made in order to incorporate this code:

  - The addition of a simplified gluos.h to eliminate operating system
    dependencies.

  - The removal of inclusion of GL/glu.h and replacement with an
    include of internal_glu.h.

  - Includes were modified to be scoped within thirdparty/glu/ and
    thirdparty/glu/libtess/.

  - The entry points to the tessellator were prefixed with internal_
    to avoid symbol collisions with any host OS version of GLU.

  - In tess.c, the obsolete entry points gluBeginPolygon,
    gluNextContour and gluEndPolygon in tess.c were #if 0'd out.
    Default branches were added to the switch statements in GotoState.

  - In memalloc.h, the include of malloc.h was changed to an include
    of stdlib.h.

  - In normal.c, an unused variable "w" was removed from
    __gl_projectPolygon. #if guards were placed around the definition
    of the unused Normalize function.

  - In priorityq-heap.c, an #include of <limits.h> was added.