The wireproto.wireprotocommand decorator is the preferred mechanism for
registering wire protocol commands. In addition, wireproto.commands
is no longer a 2-tuple and use of that 2-tuple API should be considered
This commit ports largefiles to use wireproto.wireprotocommand()
and ports to the "commandentry" API.
As part of this, the definition of the "lheads" wire protocol
command is moved to the proper stanza.
We stop short of actually using wireprotocommand as a decorator
in order to minimize churn. We should ideally move wire protocol
commands to the registrar mechanism. But that's for another