[Review Only] XD-812 Tapping named channel streams

Support for tapping named channels and streams whose source is a named
channel.

This isn't correct as it stands, particularly wrt the lifecycle of
the taps. There will be problems if the same named channel is used more
than once. For example, creating a stream

queue:blah > log

will create the tap when the log module is deployed. When it is destroyed,
the tap will be removed. If in the meantime we had created another stream

queue:blah > file

then this would be a problem.