INT-3308 SubscribableChannel Optimization

JIRA: https://jira.springsource.org/browse/INT-3308
INT-3308 Move Optimization to AbstractDispatcher

- avoids the need for `canShortCutDispatcher()`
- optimizes all framework channels, including AMQP, JMS
- slight additional performance improvement
INT-3308 FinalSingleHandlerChannel

This is still a work in process.

TODO:Parser, parser tests.

See the DirectChannelTests for perforance results.
INT-3308 'Final' Channel Parser Changes, Tests
INT-3308 Polishing; PR Comments