Marc-Andre Lemburg:

* string_contains now calls PyUnicode_Contains() only when the other
  operand is a Unicode string (not whenever it's not a string).

* New format style '%r' inserts repr(arg) instead of str(arg).

* '...%s...' % u"abc" now coerces to Unicode just like
  string methods. Care is taken not to reevaluate already formatted
  arguments -- only the first Unicode object appearing in the
  argument mapping is looked up twice. Added test cases for
  this to test_unicode.py.