commitbuilder should raise RootMissing if root was not added

[Jelmer Vernooij]

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526.355 opening working tree '/tmp/testbzr-LmtwOK.tmp'
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Text attachment: traceback
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Traceback (most recent call last):
File "/usr/lib/python2.7/dist-packages/testtools/runtest.py", line 169, in _run_user
return fn(*args, **kwargs)
File "/usr/lib/python2.7/dist-packages/testtools/testcase.py", line 508, in _run_test_method
return self._get_test_method()()
File "/home/jelmer/bzr-alltests/bzr.dev/bzrlib/tests/per_repository/test_commit_builder.py", line 209, in test_commit_without_root_errors
self.assertRaises(errors.RootMissing, do_commit)
AssertionError: RootMissing not raised