Debugging Tips
   Normally Mesa (and OpenGL) records but does not notify the user of
   errors.  It is up to the application to call
   
glGetError to check for errors.  Mesa supports an
   environment variable, MESA_DEBUG, to help with debugging.  If
   MESA_DEBUG is defined, a message will be printed to stdout whenever
   an error occurs.
   More extensive error checking is done when Mesa is compiled with the
   DEBUG symbol defined.  You'll have to edit the Make-config file and
   add -DDEBUG to the CFLAGS line for your system configuration.  You may
   also want to replace any optimization flags with the -g flag so you can
   use your debugger.  After you've edited Make-config type 'make clean'
   before recompiling.
   In your debugger you can set a breakpoint in _mesa_error() to trap Mesa
   errors.
   There is a display list printing/debugging facility.  See the end of
   src/dlist.c for details.
