Cray J90 fixes for long ints.

This was a convenient excuse to create the pyport.h file recently
discussed!
Please use new Py_ARITHMETIC_RIGHT_SHIFT when right-shifting a
signed int and you *need* sign-extension.  This is #define'd in
pyport.h, keying off new config symbol SIGNED_RIGHT_SHIFT_ZERO_FILLS.
If you're running on a platform that needs that symbol #define'd,
the std tests never would have worked for you (in particular,
at least test_long would have failed).
The autoconfig stuff got added to Python after my Unix days, so
I don't know how that works.  Would someone please look into doing
& testing an auto-config of the SIGNED_RIGHT_SHIFT_ZERO_FILLS
symbol?  It needs to be defined if & only if, e.g., (-1) >> 3 is
not -1.

Include/Python.h

@@ -31,6 +31,7 @@ redistribution of this file, and for a DISCLAIMER OF ALL WARRANTIES.
 
 #include "patchlevel.h"
 #include "config.h"
+#include "pyport.h"
 
 /* config.h may or may not define DL_IMPORT */
 #ifndef DL_IMPORT	/* declarations for DLL import/export */