Unhandled exception in trial at result reporting time

[exarkun]

Setting a `.skip' attribute to a non-string causes this traceback at the end of
a trial run in some circumstances:

Traceback (most recent call last):
  File "/usr/bin/trial", line 35, in ?
    run()
  File "/home/exarkun/projects/python/Twisted/trunk/twisted/scripts/trial.py",
line 677, in run
    suite = reallyRun(config)
  File "/home/exarkun/projects/python/Twisted/trunk/twisted/scripts/trial.py",
line 642, in reallyRun
    return call_until_failure(_doRun, config)
  File "/home/exarkun/projects/python/Twisted/trunk/twisted/scripts/trial.py",
line 627, in call_until_failure
    suite = f(*args, **kwargs)
  File "/home/exarkun/projects/python/Twisted/trunk/twisted/scripts/trial.py",
line 640, in _doRun
    suite.run(config['random'])
  File "/home/exarkun/projects/python/Twisted/trunk/twisted/trial/runner.py",
line 268, in run
    self.reporter.endSuite(self)
  File "/home/exarkun/projects/python/Twisted/trunk/twisted/trial/reporter.py",
line 276, in endSuite
    self._reportFailures(tstats)
  File "/home/exarkun/projects/python/Twisted/trunk/twisted/trial/reporter.py",
line 263, in _reportFailures
    self.write(itrial.IErrorReport(meth))
  File
"/usr/local/stow/python2.3-zope.interface/lib/python2.3/site-packages/zope/interface/interface.py",
line 675, in __call__
    adapter = self.__adapt__(obj)
  File
"/usr/local/stow/python2.3-zope.interface/lib/python2.3/site-packages/zope/interface/interface.py",
line 743, in __adapt__
    adapter = hook(self, obj)
  File "/home/exarkun/projects/python/Twisted/trunk/twisted/trial/__init__.py",
line 68, in _hook
    return factory(ob)
  File "/home/exarkun/projects/python/Twisted/trunk/twisted/trial/adapters.py",
line 218, in formatError
    ret.append(msg + '\n')
TypeError: unsupported operand type(s) for +: 'bool' and 'str'

[radix]

I made the obvious fix to this; resolving.