Port test_unicode.py to PyUnit and add tests for error

cases and a few methods. This increases code coverage
in Objects/unicodeobject.c from 81% to 85%.
(From SF patch #662807)

Lib/test/output/test_unicode

-test_unicode
-Testing Unicode comparisons... done.
-Testing Unicode contains method... done.
-Testing Unicode formatting strings... done.
-Testing builtin unicode()... done.
-Testing builtin codecs... done.
-Testing standard mapping codecs... 0-127... 128-255... done.
-Testing Unicode string concatenation... done.
-Testing Unicode printing... abc
-abc def
-abc def
-abc def
-abc
-
-abc
-abc
-def
-
-def
-
-done.