Merge pull request #1405 from takluyver/xunit-monkeypatch-on-request

Only monkeypatch xunit when the tests are run using it.

Sidesteps weird issues seen on Ubuntu buildbots.

IPython/testing/iptest.py

@@ -407,7 +407,7 @@ def run_iptest():
     and accepts all of the standard nose arguments.
     """
     # Apply our monkeypatch to Xunit
-    if not hasattr(Xunit, 'orig_addError'):
+    if '--with-xunit' in sys.argv and not hasattr(Xunit, 'orig_addError'):
         monkeypatch_xunit()
 
     warnings.filterwarnings('ignore',