Major check-in of changes for GL_EXT_framebuffer_object extension.

Main driver impacts:
- new code for creating the Mesa GLframebuffer
- new span/pixel read/write code
Some drivers not yet updated/tested.

include/GL/glfbdev.h

@@ -62,7 +62,10 @@ extern const char *
 glFBDevGetString( int str );
 
 
-extern const void *
+typedef void (*GLFBDevProc)();
+
+
+extern const GLFBDevProc
 glFBDevGetProcAddress( const char *procName );