trial -u leaks memory

New submission from exarkun <[email protected]>:

This can be observed by running the following test suite:

{{{
#!python
from twisted.trial.unittest import TestCase

class Empty(TestCase):
    def test_empty(self):
        pass
}}}

like this:

{{{
exarkun@charm:/tmp$ trial -u test_empty.py
}}}

The cause seems to be some additional (#3786) threadpool hackery in trial.

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Type     : regression
Component: trial
Keywords : 
Priority : highest
Nosy     : 
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http://twistedmatrix.com/trac/ticket/3810