Make `twisted.internet.reactor` import on Python 3

[itamar]

Given the interleaved nature of twisted.internet and its tests, we probably can't port modules in isolation. Instead, we should first make the modules necessary for the basic reactor importable. Then when we port module by module, we can do so without having broken imports make it impossible.

[itamarst]

(In [35687]) Branching to 'epollreactor-py3-5979'

[itamar]

In order for this to be useful, we probably actually want twisted.internet.reactor to be importable, which slightly expands the scope of the ticket.

[itamarst]

(In [35711]) Branching to 'epollreactor-py3-5979-2'

[itamar]

Ready for review. I tried to minimize necessary changes; probably they could've been slightly more minimal. twisted.internet.reactor imports now.

Started test run:  http://buildbot.twistedmatrix.com/boxes-supported?branch=/branches/epollreactor-py3-5979-2

[exarkun]

1. Looks like the changes to abstract.py can be dropped now
2. Not new in this branch, but default.py says "Linux: epoll(7) is the fault, since it scales well." which is correct in its way, but not what was intended I think.
3. The udp and tcp imports now hidden inside reactor methods in posixbase.py should have comments to move back up to module scope once udp and tcp are ported
4. The new SyntaxError for handling the unix import should have a similar comment, or unix should be handled the same way as udp and tcp (the latter is preferable, I think).
5. Too bad about all of the extra changes. It's pretty sad that twisted.internet.task is a dependency of twisted.internet.reactor. That dependency seems to be due to twisted.protocols.tls? Now I wish I'd worked a little harder on that module. I want to ask for some ticket for fixing this, but I can't quite figure out what the ticket is.
6. A comment about why there's a queue/Queue thing in threads.py would be nice
7. Explaining what it means that things don't subclass Ephemeral anymore would probably be nice. I bet most people have no clue what this class is or what value it provided. Just an extra clause in the news fragment, like "; incorrectly pickling these types will no longer log a warning."
8. Some conflicts in _twistedpython3.py of course

Nothing too major here. Merge when the above are addressed.

[itamarst]

(In [35735]) Branching to 'epollreactor-py3-5979-3'

[itamar]

1 and 8 were addressed by merge forward. 2, 3, 4, 6, 7 were addressed by 35737.

For IReactorUnix, I switched the check for whether to enable the interface to base it on the platformType, and moved imports in as with other tickets.

I opened ticket #6004 to deal with issue 5.

[itamar]

Started build, will merge if it's happy:  http://buildbot.twistedmatrix.com/boxes-supported?branch=/branches/epollreactor-py3-5979-3

[itamarst]

(In [35740]) Merge epollreactor-py3-5979-3.

Author: itamar Review: exarkun Fixes: #5979

Make a bunch of modules import on Python 3, port twisted.internet.default and .reactor to Python 3, and remove Ephemeral base class from a bunch of reactor-related classes.