larger scale cydonia fix.

fixes the following:

- sets the "aborted" flag properly now, so it will actually kill the units
outside the exit. area instead of dragging them along for the hell of it.

- aliens remaining on the surface will no longer follow you down into the base!

- save/load now works in the second stage of the mission, as new enemies are
given proper IDs above 100000, and leftover items are "put aside" to an invalid tile

- alien bases/cydonia will no longer have "strange holes" in 20x20 modules.

- the briefing screen will no longer be strange colours.

with thanks to Cizra for his test cases.