[RP] --command command-line option

[shawn]

you can now execute colon commands from the command line with
--command. For example to tell ratpoison to go to the next window:

$ ratpoison --command next

Its not very scalable right now. If you send 2 commands to ratpoison
before it has read the first one, it'll only execute the first one (I
think). Some reworking needs to be done, but at least something is in
there.

I still need to add options to dump the window list.

Hopefully this will allow interested parties to start writing a
keyboard driven menu system (or adapt 9menu to use the keyboard),
among other things.

I haven't tested this very hard so...test, break, patch...