Fixed bug occurring when removing Interactions (Part Deux!)

MapObject.cpp:
-Added line to decrement Interaction iterator after erasing an Interaction from the accepter's interactions vector because vector's erase method, when used on an element that isn't at the end of the vector, will cause all elements in the vector to shift left to fill the hole left by the removed element.  Additionally, I modified the end condition of the loop to be "iItr != iteractions.end()", not "iItr < iteractions.end()"; the new condition makes more sense.

Ran "./asgard scripts/demo2.py" 10 times.  All Interactions were handled properly 10/10 times.