Construction position setting function 

The commander has got the possibility to set
the location which will make the building to
the guild assigned erectors. This function
makes the constructor to build as the
commander's opinion with a systematize
strategy in the place decided.

The usual commander sets the position in the
middle land near "Mana Stone" and also
commands to build near the Mana collector.
 
Only the commander can see the position of
the "Mana Stone". If the location is not set
the constructor can't build it.