Highlights:
- Adding PyObject_Format.
- Adding string.Format class.
- Adding __format__ for str, unicode, int, long, float, datetime.
- Adding builtin format.
- Adding ''.format and u''.format.
- str/unicode fixups for formatters.
The files in Objects/stringlib that implement PEP 3101 (stringdefs.h,
unicodedefs.h, formatter.h, string_format.h) are identical in trunk
and py3k. Any changes from here on should be made to trunk, and
changes will propogate to py3k).
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