[Xmonad] Make some workspaces prefer some heads

[Kai Grossjohann]

I find that the current workspace switching model does not match my
usage pattern.  My usage pattern is that I tend to use the same head to
view a given workspace.

Is there anyone who prefers a similar working style and who could
provide code to implement it?  I know that you guys usually tell me
that I can do it myself and that it is very easy, but this time, I am
doubtful.

My working style:

  - There should be a command to say "workspace X prefers head Y" (for
    example with X being the currently focused workspace and Y the
    currently focused head).

  - When switching to a workspace, display it on the preferred head.
    (If there is no preferred head, have some rule such as to always
    show it on the second head.)

  - There should be a way to say that I want to view workspace X on the
    current head, no matter what X's preferred head is.

FWIW, I have a single workspace dedicated to full-screen windows
(currently, Firefox, OpenOffice.org and Adobe Reader) that I display on
the internal laptop display, whereas all other workspaces are usually
displayed on the external display.

This means that I can keep up with my favorite newsticker while waiting
for compilations to finish, and watch the logs while using the web
application I'm developing.

However, from time to time I want to see a workspace with terminal
windows and a workspace with VMware at the same time, so I either move
the terminal windows workspace to the internal head, or the VMware
workspace to the internal head.

Kai