[ogl-sample] another glcore.h change, Brian Paul, 2001/04/27

[ogl-sample] suggested change for glcore.h, Brian Paul, 2001/04/27

[ogl-sample] Bug fix for __glXSwapBuffers(), Brian Paul, 2001/04/27

[ogl-sample] Bug in GLU: invalid call to glMapGrid2f(), Diego Santa Cruz, 2001/04/23