hooking XCreateWindow and friends via LD_PRELOAD. Used now to make sure that
windows come up in the workspace they were spawn()'d from, but more soon.
Code to do the nasty borrowed with thanks from Enlightenment.
- workspaces now per-screen (X does not let you migrate windows)
- a screen has 1 or more regions (now mapped by Xrandr, later configurable)
- current_ws is dead, long live cur_focus
- only one window has real focus, but workspaces keep track ws->focus
- lots of places (especially event handlers) use cur_focus but should
identify the correct source of the event instead
- festival of pointer management to keep track of all this.
