Rationalize use of limits.h, moving the inclusion to Python.h.

Add definitions of INT_MAX and LONG_MAX to pyport.h.
Remove includes of limits.h and conditional definitions of INT_MAX
and LONG_MAX elsewhere.

This closes SourceForge patch #101659 and bug #115323.

Python/modsupport.c

@@ -2,9 +2,6 @@
 /* Module support implementation */
 
 #include "Python.h"
-#ifdef HAVE_LIMITS_H
-#include <limits.h>
-#endif
 
 #ifdef MPW /* MPW pushes 'extended' for float and double types with varargs */
 typedef extended va_double;