Allow completing partial builds even if numtypes > 1

[Hans Ronne]

>In the latter case without the patch, a unit cannot complete a
>partially built unit which it didn't start.  If the unit which began
>building is gone, you need to disband the partially built unit and
>start over.  With the patch, the behavior is similar to the former
>case.

Good point. There is a problem, however, that I ran into when I implemented
a similar fix in the advanced unit build code (run_construction). Thus,
impl_build calls net_push_build_task, which passes a unit type, not a unit.
This is no good since you want to resume building the existing incomplete
unit, not start on yet another one. I therefore added a new kernel
function, resume_build_task (and the corresponding net_resume_build_task)
which takes an existing unit as argument and sets the build task
accordingly.

So what you need to do is to call net_resume_build_task instead of
impl_build. Otherwise, your occupant will just start on a new unit with the
same type as the incomplete transport.

Hans

Hans Ronne

hronne@pp.sbbs.se