Backport of PEP 3101, Advanced String Formatting, from py3k.

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).
diff --git a/Python/formatter_unicode.c b/Python/formatter_unicode.c
new file mode 100644
index 0000000..17c6944
--- /dev/null
+++ b/Python/formatter_unicode.c
@@ -0,0 +1,13 @@
+/* Implements the unicode (as opposed to string) version of the
+   built-in formatter for unicode.  That is, unicode.__format__(). */
+
+#include "Python.h"
+#include "formatter_unicode.h"
+
+#include "../Objects/stringlib/unicodedefs.h"
+
+#define FORMAT_STRING unicode__format__
+/* don't define FORMAT_LONG and FORMAT_FLOAT, since we can live
+   with only the string versions of those.  The builtin format()
+   will convert them to unicode. */
+#include "../Objects/stringlib/formatter.h"