demogl.{c,h} - OpenGL rendering routines (this directory. Shared by
               programs in threee directories below).

The following three directories have the same "demo.c" program which
uses demogl, but is setup three different ways.

singlewin   - Window setup to render in a single window. Most normal 
              aplications work this way and don't have do anything 
              special for OpenGL 1.2, 1.3 and extension procs.

multiwin    - Multiple windows with a single message loop. At any given
              time, there is only context which is current. The application
              defines its own method for accessing the proc table 
              (see _APP_PROCTABLE flag in the Makefile). Since there is
              only window which is current, a global variable can be used
              to provide reference to the current proc table.

multithread - Multiple windows with a multiple message loops using 
              multiple threads. At any given time, there can be multiple
              current contexts.  The application defines its own method 
              for accessing the proc table (see _APP_PROCTABLE flag in 
              the Makefile). However, there can me multiple current contexts
              on different thread, the application uses thread local 
              storage to define proper access to the current proc table.