Code review comment for lp://qastaging/~gz/pyjunitxml/ensure_well_formed_xml_625589

Fails selftest:

:!python -m testtools.run junitxml.test_suite
Tests running...
======================================================================
ERROR: junitxml.tests.test_junitxml.TestWellFormedXml.test_error_with_surrogates
----------------------------------------------------------------------
Traceback (most recent call last):
  File "junitxml/tests/test_junitxml.py", line 313, in test_error_with_surrogates
    self.assertTrue(unichr(0x201A2) in traceback)
UnboundLocalError: local variable 'unichr' referenced before assignment
Ran 18 tests in 0.007s

Also has conflicts in trunk, but they are shallow.