Add documentation.

src/glu/sgi/glu.def

@@ -1,5 +1,30 @@
 DESCRIPTION 'Mesa GLU (OpenGL work-alike) for Win32'
-VERSION 4.1
+VERSION 5.1
+;
+; Module definition file for GLU (GLU32.DLL)
+;
+; Note: The GLU functions use the STDCALL
+; function calling convention.  Microsoft's
+; GLU32 uses this convention and so must the
+; Mesa GLU32 so that the Mesa DLL can be used
+; as a drop-in replacement.
+;
+; The linker exports STDCALL entry points with
+; 'decorated' names; e.g., _glBegin@0, where the
+; trailing number is the number of bytes of 
+; parameter data pushed onto the stack.  The
+; callee is responsible for popping this data
+; off the stack, usually via a RETF n instruction.
+;
+; However, the Microsoft GLU32.DLL does not export
+; the decorated names, even though the calling convention
+; is STDCALL.  So, this module definition file is
+; needed to force the Mesa GLU32.DLL to export the
+; symbols in the same manner as the Microsoft DLL.
+; Were it not for this problem, this file would not
+; be needed (for the glu* functions) since the entry
+; points are compiled with dllexport declspec.
+;
 
 EXPORTS
 	gluBeginCurve