If an event has a hotspot, use the hotspot center for the center point

This fixes triggering events that have a hotspot that isn't the event
location.
Merge pull request #1151 from dorkster/fixes

If an event has a hotspot, use the hotspot center for the center point
Show filename & line number for file parsing errors

For most instances of file parsing, I've also added error checking for
the validity of each parsed key. This should help track down obsolete
stuff in mods.