test suite should pass with -O

[daira]

bin/tahoe @python -O @tahoe debug trial --rterror
[...]
[FAIL]
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/Twisted-12.3.0-py2.7-linux-x86_64.egg/twisted/internet/defer.py", line 138, in maybeDeferred
    result = f(*args, **kw)
  File "/usr/local/lib/python2.7/dist-packages/Twisted-12.3.0-py2.7-linux-x86_64.egg/twisted/internet/_utilspy3.py", line 41, in runWithWarningsSuppressed
    reraise(exc_info[1], exc_info[2])
  File "/usr/local/lib/python2.7/dist-packages/Twisted-12.3.0-py2.7-linux-x86_64.egg/twisted/internet/_utilspy3.py", line 37, in runWithWarningsSuppressed
    result = f(*a, **kw)
  File "/home/davidsarah/tahoe/git/trunk/src/allmydata/test/test_util.py", line 485, in test_abspath_expanduser_unicode
    self.failUnlessRaises(AssertionError, fileutil.abspath_expanduser_unicode, "bytestring")
  File "/usr/local/lib/python2.7/dist-packages/Twisted-12.3.0-py2.7-linux-x86_64.egg/twisted/trial/_synctest.py", line 338, in assertRaises
    % (exception.__name__, result))
twisted.trial.unittest.FailTest: AssertionError not raised (u'/home/davidsarah/tahoe/git/trunk/_trial_temp/bytestring' returned)

allmydata.test.test_util.FileUtil.test_abspath_expanduser_unicode
===============================================================================
[ERROR]
Traceback (most recent call last):
  File "/home/davidsarah/tahoe/git/trunk/src/allmydata/test/common_util.py", line 109, in done
    (which, expected_failure, res))
twisted.trial.unittest.FailTest: test_shares_by_server was supposed to raise <type 'exceptions.AssertionError'>, not get '{'1': set([1]), 's': set([1]), 'r': set([1]), 'e': set([1]), 'v': set([1])}'

allmydata.test.test_upload.EncodingParameters.test_shares_by_server
===============================================================================
[ERROR]
Traceback (most recent call last):
  File "/home/davidsarah/tahoe/git/trunk/src/allmydata/test/common.py", line 1064, in done
    (which, expected_failure, res))
twisted.trial.unittest.FailTest: test_compute_rate was supposed to raise <type 'exceptions.AssertionError'>, not get '-10.0'

allmydata.test.test_web.Util.test_compute_rate
allmydata.test.test_web.Util.test_compute_rate
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