Support channel-or-user IRC commands, and setup irc-msg to use it.

Signed-off-by: Edward Z. Yang <ezyang@mit.edu>
Added a perl hook for :away

Note: The sepbar no longer distinguishes between AWAY, A-AWAY, and
Z-AWAY.
Added a hook for wakeup/user input.

I wanted to add a hook that got called on all user-input, but any
non-trivial use of that hook incurred too much overhead (about 7 ms per
paragraph for entry into perl, and another 100 ms or so per paragraph
for execution of the hook; tests run on pasting lorem ipusm, on
linerva).

This hook is called at most once a second (approximately).
Added perl methods to register and unregister idle watchers.