Removing 'import as' import style

The style of import used for qpid.messaging objects used 'import foo as bar' style.  This was no easy for the mock module in test code to find as a patchable target.  I've redone the imports to live in their proper location.
Small docstring class path

Path to qpid.messaging.exceptions was wrong in docstrings
Redoing the imports for RELEASED and REJECTED

These objects can be mocked properly by redoing the imports in this way
Three new classes, removing old amqp stuff.

New test classes include Connection, FDShimThread, and FDShim.