[Twisted-Python] A new testing strategy for protocols

[Itamar Shtull-Trauring]

A long time issue we've had is how to test protocols under "real" 
circumstances. For DNS testing, I decided to do just that - see the code 
in twisted/test/test_names.py.

Basically, I start a server listening using UDP, and have a client 
connect to it, all within the testing code and automatically. It works 
pretty well, after a bit of debugging. Data is pushed by calling 
main.iterate().

Now, in a lot of cases twisted.protocols.loopback may be good enough, 
but this approach is really necessary for thorough testing in certain 
cases. FTP leaps to mind, but also if we want automated testing of TOC 
or OSCAR clients against real servers.

One drawback at least is that these tests will fail miserably on Jython 
(main.iterate on Jython doesn't push data), so I'm probably going to add 
code that makes sure they don't run at all on Jython.

Another drawback is the related issue that I'm also testing DNS queries 
against real servers - this assumes a working net connection.