CRT Combat Model (really long)

[Jim Kingdon]

> > [orc-holes and such get partially built and then not finished]
> 
> This is a known bug. I fixed it at one point in the advanced unit build
> code, by writing a special resume_build_task function. However, the fix was
> lost later when this code was merged with the general build code.

This happens a lot in the standard game with bases.

It would be nice to fix - I wonder how much the AI in the standard
game would extend its geographical reach by building bases.  I do
realize that the selection of where to build a base would still be
pretty haphazard, as build_depot_for_self isn't particularly
sophisticated.