Initial changes to move tmux to libevent.
This moves the client-side loops are pretty much fully over to event-based only
(tmux.c and client.c) but server-side (server.c and friends) treats libevent as
a sort of clever poll, waking up after every event to run various things.
Moving the server stuff over to bufferevents and timers and so on will come
later.
Add an activity time for clients, like for sessions, and change session and
client lookup to pick the most recently used rather than the most recently
created - this is much more useful when used interactively and (because the
activity time is set at creation) should have no effect on source-file.
Based on a problem reported by Jan Johansson.
Change session and client activity and creation time members to have more
meaningful names.
Also, remove the code to try and update the session activity time for the
command client when a command message is received as is pointless because it
des not have a session.
Don't do anything in the client callback if the client has already died to
avoid a use-after-free (the callback is used twice, once for the client itself
and once for the tty). Fixes crashes seen by Han Boetes.
Remove the -d flag to tmux and just use op/AX to detect default colours.
Irritatingly, although op can be used to tell if a terminal supports default
colours, it can't be used to set them because in some terminfo descriptions it
resets attributes as a side-effect (acts as sgr0) and in others it doesn't, so
it is not possible to determine reliably what the terminal state will be
afterwards. So if AX is missing and op is present, tmux just sends sgr0.
Anyone using -d for a terminal who finds they actually needed it can replace it
using terminal-overrides, but please let me know as it is probably an omission
from terminfo.
Split the server code handling clients, jobs and windows off into separate
files from server.c (merging server-msg.c into the client file) and rather than
iterating over each set after poll(), allow a callback to be specified when the
fd is added and just walk once over the returned pollfds calling each callback
where needed.
More to come, getting this in so it is tested.
