[FR] Bugger-off improvement

Here's a black factory with a cyan bugger-off (the cyan sphere can be seen in `/debugcolvol` view). Units buggering off will move to a random point in a larger circle around it (here marked orange, and I don't think it is visualisable).

In particular, sometimes units will move all the way around behind the factory. This is especially bad for constructors guarding the factory because then they often have to come back to be in range of the build-pad.

The request is essentially to stop this from happening in some way. A powerful way would be to make the bugger off target also a configurable circle:

Some cheap-ass hack such as rejecting paths that intersect the unit ordering the bugger off and rolling another spot would probably also be fine.

Reproduce the behavior in the `/debugcolvol` view, focusing on units buggering off around factories and constructors guarding them. Trace the movement and path-selection entry points involved in choosing the bugger-off target; done means units no longer take the undesirable route while still reaching a valid nearby position.

Written by the indexing model from the issue text.