Add MockCellChannel.java for testing
Add NodeConnectionOpenerTest.java
Add NodeConnectionOpenRequestTest.java
Add NodeConnectionTest.java
Add Circuit.java
Implement NodeConnection.Opener
Fix bug in MockCellChannel

 - Previously threw an AssertionError as a mock; should
   throw a ProtocolException as expected behavior.
Implement NodeConnection.OpenRequest
Remove test-related inner class from NodeConnection
Bound the read() loop in NodeConnectionTest
Allow CellParser.expectFromStream() to match subtypes
Replace MockCellChannel with EasyMock
Add incoming message tests for NodeConnectionTest
Fix bugs in NodeConnectionTest
Implement NodeConnection demultiplexer
Put this commit into fixbugs for nct