I seem to recall that despite the C standards, there are platforms around
where isdigit and isxdigit are still locale aware.  This bit me when I 
implemented float.fromhex:  see r65964.

And my man page for isdigit says:

COMPATIBILITY
     The 4.4BSD extension of accepting arguments outside of the range of 
the unsigned char type in locales with large character sets
     is considered obsolete and may not be supported in future releases.  
The iswdigit() function should be used instead.


So I'm tempted to go the other way and say that all uses of isdigit should 
be replaced by ISDIGIT.


I'll fix the Py_CHARMASK and move remove_trailing_zeros inside the ifdef.