Changes to merge with Win32 edwin screen driver and support.

Changes to merge with Win32 edwin screen driver and support.

The main change is the addition of a new Edwin screen device for
Win32.  The new device implements special keys and mouse buttons.  A
certain degree of reorganization has been done to make the X and Win32
versions as similar as possible.  Some things that used to be called
X-MUMBLE are now just called MUMBLE (e.g BUTTON1-UP, MOUSE-SET-POINT).

New files:
  win32.scm:     New screen device
  win32com.scm:  Win32 specific commands
  key-w32.scm, key-x11.scm:  System specific handling of special keys
    (arrows etc).  These files replace key.scm
  mousecom.scm: mouse commands, edited from xcom.scm

Notable changes:
  calias.scm: much of the old key.scm was moved here.  Now the keys
    `f1', `up' etc are available in all Edwins, even if the keyboard
    cannot generate them.  (I have a prototype fix for the console
    screen driver too).

  debug.scm, modefs.scm, xmodef.scm: renamed and/or reorganized
    bindings

  xcom.scm: A whole lot of this moved to mousecom.scm