Session management and retry improvements.

Session management and retry improvements.

Lots of improvements and several bug fixes.

Previously managed clientwas returning the underlying session client instead 
of retry, so retry wasn't enabled for uses trying to catch/store the client from 
connect.

The retry code was using seconds for session timeout instead of milliseconds. 

The retry code wasn't taking account of the start of retry properly when 
determining max retry.

The retry on persistent error wasn't signaling to the managed client to 
establish a new session.

The client code wasn't properly cleaning up txzk handles on conn timeouts.

The session establishment now uses the client session events so even without 
activity or active watches the session is restablished.

Session restablishment will now backoff on reconnects for up to 6m.

https://code.launchpad.net/~hazmat/txzookeeper/backoff-retry-managed-sanity/+merge/146938

(do not edit description out of merge proposal)

[hazmat, 2013-02-06 19:27:59]

Please take a look.

[hazmat, 2013-02-06 19:30:06]

Please take a look.

[hazmat, 2013-02-07 00:06:12]

Please take a look.