Fix part of SF bug # 544248 gcc warning in unicodeobject.c
Fix part of SF bug # 544248 gcc warning in unicodeobject.c

When --enable-unicode=ucs4, need to cast Py_UNICODE to a char

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator