[AD] loss of videoBitmap after set_gfx_mode()

[aj <aj@xxxxxxxxxx>]

1. set_gfx_mode()
2. then i create a video bitmap
3. everything works OK.
4. then i set_gfx_mode()  to something else
5. everything is OK.
6. then i go to exit my program.
7. my exit routine destroys all my bitmap*  that are != NULL
8. my video_bitmap*  != NULL
9. call  destroy_bitmap()  on it
10.  CRASH!

the error message MSVC debugger offers me says something about memory not 
read/write-able  at 0xcdcdcdcd
that 0xcdcdcdcd  looks like someone's idea of an obvious value....

i read the docs (WIP415)  at  set_gfx_mode()  and i read the 
create_video_bitmap()  and no mention of this anomolly there either.
i even looked under destroy_bitmap()  and no mention of it there either.


solutions:
1.  fix the anomolly.

2.  add some comments to the docs.
suggestion:  (at the end of the create_video_bitmap() docs)
  "Warning: video bitmaps may be lost after a set_gfx_mode() call."

3.   ?



aj.