Fix proxy error condition and simplify method

Add new minion proxy test case.
Address remaining comments from #756

Rename Encoding to Codec, Versioning to ResourceVersioner.  Add
GoDoc.  Add Delete(key, recursive) to EtcdHelper
Merge pull request #808 from smarterclayton/minion_proxy_test

Fix proxy error condition and simplify method
Merge pull request #806 from smarterclayton/follow_up_to_encoding_abstraction

Address remaining comments from #756
Add more parameters to Watch

* Add labels selector (same as List)
* Add fields selector
 * Plan to let you select pods by Host and/or Status
* Add resourceVersion to let you resume a watch where you left off.
Allow more general parameters to be made by client. Also fix style and comments.
Add fake client to make testing easier.
Add WatchReplicationControllers to kubecfg's fake
Make replication controller use client
Simplify ResourceWatcher interface to one function.