Walls not build if wall tower foundations overlap

[elexis]

As noticed by temple spectating a Hellas game with Emperior, it can occur that wall pieces are not being built following ​Phab:D21 if the obstructions of the wall tower foundations overlap.

This regression must be fixed before the release. The easiest way to accomplish that is making structures not block construction as proposed in ​Phab:D1445 (and the case in a22).

But there is also the question if this ideal. It'd be better if foundations cannot overlap (which was an assumption of ​Phab:D21.)

There is a patch for the templatesanalyzer detecting incompatible lengths at ​Phab:D1440. ​Phab:D1439 changes wall tower lengths to match the obstruction size.