Comment 22 for bug 977980

I think we should aim for some behavior that is similar to the current one. I think it is:
- fish: one triangle is enough (reason in #19)
- mountain resources: four matching triangles
- water: no idea

I also don't know if dead terrain (lava) has/should have an influence on this.

Resources that do not match the new terrain combination should be removed automatically, so there is acutally never a need to remove them manually.