migrated to netty 4.0.4

As netty 4 API has been fixed now, I made lettuce working with netty 4.0.4.Final.

This passes all 219 passes with no complaints, in Mac OS X 10.8.4 / Java 1.7.0_11.

Aside from find-and-replace changes, there are a few changes like

- `ChannelInitializer` instead of `ChannelPipelineFactory` and simplified `ConnectionWatchdog.run()`
- `@ChannelHandler.Sharable` annotation to each `ChannelHandler` classes, to make the multiplicity checker happy during reconnection
- Manually releasing ByteBuf, as netty 4 requires it, as well as manual HashedWheelTimer stopping
- `Command.output != null` checks to safely ignore responses from timed out commands. This makes the `ClientTask.timeout()` the happy


Please review the changes and I'd be happy to have it merged to your repository, or possibly in a separate branch for netty 4.

Many thanks for making this awesome library!