CallError rather than trying to preserve exceptions.
Dead sentinel value instead of killed everywhere.
Simplify Channel.
MasterModuleResponder error response.
Simplify Unpickle().
Simplify reprs everywhere.
AllowClass() instead of AllowModule().
Get rid of needless property().
Split ExternalContextMain up into class.
econtext.utils module.
* Tidy up docstrings.
* Start work on IoLogger and LogForwarder.
* Fix race in Stream.Accept / AddHandleCb CALL_FUNCTION
* Fix stdout slave stream corruption.
* Fix HOSTNAME vs. socket.gethostname().
* Remove silly locking.
* Move handle management to Context for later reconnects.