This implements PEP 3101, for the py3k branch.

Known issues:
Better error handling, per the PEP.

Need to write Formatter class.

test_long is failing, but I don't think it's my doing.

Need to fix this warning that I introduced when compiling
Python/formatter_unicode.c:
Objects/stringlib/unicodedefs.h:26: warning: `STRINGLIB_CMP' defined but
not used

Need more tests for sign handling for int and float.

It still supports "()" sign formatting from an earlier PEP version.