Replacement for wind.o

[John R. MacMillan]

 [in reference to screen blanker for MGR]

|The only tricky part is that the rest of the code needs to respect the blanked
|status, and only write changes to the memory images of the windows, and not
|to the screen.  But I'll get it!

One way to do this at the cost of some memory is to have memory for a
screen, and switch the pointer that the bitblt routines write through
to point at this memory when the screen is blank, or the real screen
the rest of the time.  (``All problems in computer science can be
solved by adding another layer of indirection'' -- Unknown).

So the blankout routine would look like:

- copy video_screen to save_screen
- set screen = save_screen

And to unblank:

- copy save_screen to video_screen
- set screen = video_screen

|3. My new job has me writing bit blit routines in assembly languages all day
|long.  What's one more?  I'm going to code all of mgr's bitblits in 68010
|assembler and get this baby cookin'.

Yeehaw!  I'll name my first-born David...