Type checking of swap/over/etc.

[GalHorowitz]

Currently The type checker handles the swap operation by just popping the (type, location) tuple from the type stack and then pushing the tuples back in the new order, but this means the source location in the tuple doesn't change, i.e. the arguably real source of the element (the swap operation) is not recorded. Is this really the intended behavior?

This is not limited to the SWAP operation of course