Ungarrison units in the direction of their garrisonholders rallypoint

[Imarok]

When the initial spawnpoint of a building is unconnected with the rest of the map, you won't be able to use the units from this building, because they are trapped inside this unconnected area. This often happens when you build a fortress near some trees and train some rams.

In this picture, we see a catapult being trained, but it's trapped inside some trees, because it spawns at the initial spawnpoint of the fortress (red circle):

The solution to this issue is to set the inital spawnpoint at the position, their is in.

refs #4484