adding some basic mouse support to switch frame

Hello,

I am a new user of ratpoison, and so far I love it! So first thing,
thanks a lot for this great software!

I would like to add some basic support to be able to switch frame using
the mouse. It should be configurable, I do not intend to change the
default behavior. I was thinking about a new variable, let's say
'mousefocuspolicy', which could take some values:

- "none": this is the current behavior
- "click": allow to select the frame under the mouse when the user click
- "move": (maybe this can be done later, I am not sure of that yet) this
  would select the frame automatically under the mouse, when the user
  move it

It could then be used easily in the configuration file:

set mousefocuspolicy click


Note that I am aware of the sloppy.c file, but I find it too intrusive,
and it does not exactly fix my need I believe.

I started to look at the code, and those changes will require the
ratpoison windows to listen to some new x events (using
ButtonMotionMask, and I think EnterWindowMask or maybe PointerMotionMask
for the "move" value).


Anyway, before going further, I would like to hear what you think of
it. Does it sounds interesting? I would be happy to implement it
(without the "move" value for now) if that sounds good to you.

Cheers,

-- 
~Julien