Builders get stuck forever trying to build, if an animal is in the way

[frapell]

Steps to reproduce:

1) Grab a bunch of workers 2) Select a building 3) Place the building over an animal, such as a deer

What happens:

The animal stays still, builders start hammering, and the building doesn't advance in its construction.

What should happen:

Animals should flee when workers approach, or at least move away if there's a building starting where they are standing.

SVN revision: 14494.