Apart from the CMusicRoom music, the game doesn't differentiate between
music and sound effects. This adds an optional _soundType field to the
CProximity class, so I can manually specify which is which
Turns out that some of the messages have properties that the objects
that handle them can set. For example, the CMouseDragStartMsg has a
_dragItem property that an item that allows dragging will explicitly
set, allowing the input handler to keep track of what was dragged.
Paul Gilbert