Port twisted.internet.error to Python 3

[itamar]

twisted.internet.error needs to run on Python 3.3.

[itamarst]

(In [35629]) Branching to 'ierror-py3-5972'

[itamar]

The getConnectError API does not appear to be used well in Twisted, e.g. I'm pretty sure the gaierror code path is never hit. But, at least there's tests now. The changes to the code were because Python 3 doesn't have __getitem__ on Exceptions anymore.

 http://buildbot.twistedmatrix.com/boxes-supported?branch=/branches/ierror-py3-5972 was started, haven't looked at it yet.

[exarkun]

1. in test_error.py, please move the stdlib imports above the twisted imports.
2. in error.py, perhaps the comment about Python 2.2 could be adjusted? It seems like the author probably meant "Python 2.2 and newer", which effectively means all Python versions now. I suspect socket.gaierror is always present now, too, but we can leave actually changing the logic for another time (file a ticket?)

Otherwise looks good, please merge after addressing the above.

[itamar]

Will do. (I couldn't BTW find any instance where an actual exception was passed in, only tuples, but maybe I missed something.)

[itamarst]

(In [35643]) Merge ierror-py3-5972

Author: itamar Review: exarkun Fixes: #5972

Port twisted.internet.error to Python 3, with improved test coverage.