Setting the 'getIterator' argument drops the memory usage of calling
get_network_status by 71% (from 3.5 MB to 1 MB). This is still higher than what
I was expecting from a generator, though certainly much better.

Unfortunately this didn't have an impact on the ConsensusTracker. The memory
usage from its constructor dwarfs anything else I've looked at (18.8 MB) and
didn't drop like I'd expect when consensus_only was false. :(

When we attempt to initiate a control connection to a non-control port (for
instance tor's socks port instead)...
- the socket shutdown issues an error since it's not connected yet
- checking the authentication type fails with a TorCtlClosed rather than error
  reply

For more information see bug 2580.

When the signal sent by _sendImpl causes the control connection to close we
block indefinitely waiting for a response. For more information see bug 1329.

Event listening, particularly BW events, is a common request on irc so using it
as the TorCtl example. For more information see bug 2065.

Each TorCtl instance spawned a socket that would continue to live for the life
of the python process. For more information see ticket 2812.

When shutting down we can't join on _thread unless the socket receives data
because we didn't have a timeout. This issues a 20 ms timeout on socket reads
and cleans up _thread when we close.

Also remove some traceback debugging statements.

It may be silently killing the bwauths on some platforms..