Fix regression in reconnect logic.

Very much need automated tests for reconnection and queue logic.

Many contributed fixes. Thanks everybody.

* [redisGH-127] - properly re-initialize parser on reconnect
* [redisGH-136] - handle passing undefined as callback (Ian Babrou)
* [redisGH-139] - properly handle exceptions thrown in pub/sub event handlers (Felix Geisendörfer)
* [redisGH-141] - detect closing state on stream error (Felix Geisendörfer)
* [redisGH-142] - re-select database on reconnection (Jean-Hugues Pinson)
* [redisGH-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
* [redisGH-140] - support optional callback for subscribe commands
* Properly flush and error out command queue when connection fails
* Initial work on reconnection thresholds

Fix and test for [redisGH-123]

Passing an Array as as the last argument should expand as users
expect.  The old behavior was to coerce the arguments into Strings,
which did surprising things with Arrays.

Contributed changes:

*  Support SlowBuffers (Umair Siddique)
*  Add Multi to exports (Louis-Philippe Perron)
*  Fix for drain event calculation (Vladimir Dronnikov)

Thanks!

Bugs fixed:

*  authentication retry while server is loading db (danmaz74) [redisGH-101]
*  command arguments processing issue with arrays

New features:

*  Auto update of new commands from redis.io (Dave Hoover)
*  Performance improvements and backpressure controls.
*  Commands now return the true/false value from the underlying socket write(s).
*  Implement command_queue high water and low water for more better control of queueing.

See `examples/backpressure_drain.js` for more information.

Add support and tests for Redis scripting through EXEC command.

Bug fix for monitor mode.  (forddg)

Auto update of new commands from redis.io (Dave Hoover)

Lots of bugs fixed.

*  connection error did not properly trigger reconnection logic [redisGH-85]
*  client.hmget(key, [val1, val2]) was not expanding properly [redisGH-66]
*  client.quit() while in pub/sub mode would throw an error [redisGH-87]
*  client.multi(['hmset', 'key', {foo: 'bar'}]) fails [redisGH-92]

Added DISCARD

I originally didn't think DISCARD would do anything here because of the clever MULTI interface, but somebody
pointed out to me that DISCARD can be used to flush the WATCH set.

Added missing HVALS command

Fix bug with empty Array arguments - Andy Ray