. Updated GL/gl.h with GLCALLACKP and GLAPIENTRYP macros for compatibility

 . Updated GL/gl.h with GLCALLACKP and GLAPIENTRYP macros for compatibility
   with the IBM VisualAge C++ compiler. Eventually some more code will be
   needed in the headers to enable the reversal of (__stdcall*) to (*__stdcall)
   for the IBM compilers, however we currently build using our own header files
   that already handle this.

 . Changed instances of (GLCALLBACK*) to GLCALLBACKP for compatibility
   with the IBM VisualAge C++ compiler in src-glu.

 . Misc cleanups for warnings generated with Watcom C++ in src-glu. Compiles
   with 0 warnings now.

 . tess_hash.c: line 244 - Why is this function stubbed out? I removed the
   code with a #if 0 to avoid a compiler warning, but it looks dangerous.