PyString_Concat() and PyString_ConcatAndDel() (the name PyUnicode_Concat()
was already taken).
Change PyObject_Repr() to always return a unicode object.
Update all repr implementations to return unicode objects.
Add a function PyObject_ReprStr8() that calls PyObject_Repr() and converts
the result to an 8bit string.
Use PyObject_ReprStr8() where using PyObject_Repr() can't be done
straightforward.
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