improving multi-monitor support in x11/carbon

[Yuri D'Elia]

Hi everyone. Currently emacs 21.x (and 22) lacks decent support for 
multi-monitors setups.

x-display-* functions simply return the whole viewable area which spans 
across several monitors. This breaks maximization and window 
positioning: the window will cover all monitors (and sometimes not 
correcly) and will not always position on the same monitor.

There has been some discussion already, here:

http://lists.gnu.org/archive/html/bug-gnu-emacs/2008-01/msg00165.html
http://lists.gnu.org/archive/html/bug-gnu-emacs/2008-02/msg00006.html 

and here:

http://lists.gnu.org/archive/html/emacs-pretest-bug/2007-03/msg00412.html

I fully agree with Yamamoto Mitsuharu here: a clear designed api is 
needed:

- there may be more than a single monitor
- placement and size may not be linear or constant
- the origin can be anywhere, not simply at +0+0
- viewable area may not be the the whole screen:
  - on mac there is a menu bar on the main monitor only
  - on windows there's the start panel, which may or may not occupy space

(and possibly other issues that I forgot).

Yet, the current behavior needs some fixing in order to be of any use. I 
think that x-display-* functions should return, for the time being, the 
size of the _current_ monitor, the one on which the current frame is 
shown.

Is that feasible?

Thanks