[Twisted-Python] Trial Refactoring

[Jonathan Lange]

I've made some pretty significant changes to trial tonight [1][2]. They 
have been mainly focussed on refactoring to reduce repeated code, and 
on being able to extend trial.

The tests work for me [3]. If they don't work for you, this is probably 
the reason. Please check for your platform as soon as possible and let 
the list know.

I have tried hard to keep the functionality as close to the original as 
possible, but there have been some changes.

Feel free to gaffle me and rollback the commit if this is a disastrous 
mistake.

cheers,
jml

[1] 
http://twistedmatrix.com/users/jh.twistd/viewcvs/cgi/viewcvs.cgi/twisted/trial/unittest.py.diff?r1=1.63&r2=1.64&cvsroot=Twisted
[2] 
http://twistedmatrix.com/users/jh.twistd/viewcvs/cgi/viewcvs.cgi/twisted/trial/unittest.py.diff?r1=1.64&r2=1.65&cvsroot=Twisted
[3] In Python 2.2. In Python 2.1, testPackages in test_doc fails. I     
don't think this is my fault.