Many contributed fixes. Thanks everybody.

* [GH-127] - properly re-initialize parser on reconnect
* [GH-136] - handle passing undefined as callback (Ian Babrou)
* [GH-139] - properly handle exceptions thrown in pub/sub event handlers (Felix Geisendörfer)
* [GH-141] - detect closing state on stream error (Felix Geisendörfer)
* [GH-142] - re-select database on reconnection (Jean-Hugues Pinson)
* [GH-146] - add sort example (Maksim Lin)

Some more goodies:

* Fix bugs with node 0.6
* Performance improvements
* New version of `multi_bench.js` that tests more realistic scenarios
* [GH-140] - support optional callback for subscribe commands
* Properly flush and error out command queue when connection fails
* Initial work on reconnection thresholds
