HOpenGL uses wrong calling convention for GLU callbacks

[nobody]

on windows (seen on 98&xp), the red book examples
Tess and TessWind (from GLUT/examples/RedBook/)
crash with a segv. 

Fix (tested on win xp only): 
in 
OpenGL/Graphics/Rendering/OpenGL/GLU/Tesselation.h
s, 
change ccall to CALLCONV (which will be stdcall in this 
case) for all foreign import "wrapper" callback generators.

http://www.haskell.org//pipermail/hopengl/2005-
April/000610.html

claus.reinke@talk21.com

[spanne]

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There seems to be a discrepancy between the GLU header shipped 
with X11 and with MinGW regarding this aspect, but applying the 
proposed change seems to be safe because only WinDoze will be 
affected. 
 
Quadrics and NURBS have a similar issue, BTW.