Another Direct X Caverot test version

[Olly Betts]

Okay, I've had a bash at fixing the niggles - this new version should
hopefully:

* produce output for "caverot --help".

* redraw the display if you switch away and back with alt-tab (the timing
  will be messed up though so it'll probably jerk wildly before settling
  down).

* run in a window if run as "caverot --window olly.3d".

* bring up a mode picker dialog if run as "caverot --mode-picker olly.3d".

But I can't actually check any of these, so again please treat with caution
(save unsaved work, etc):

http://www.survex.com/software/test/wincvrot2.zip

Josep tells me that his problem with not getting any display at all seems to
have been fixed by one of the minor changes I made in 0.96-prerelease3, so
things are looking good.

Cheers,
Olly