Event-based difficulty

[Jens Granseuer <jensgr@gmx.net>]

There hasn't been much input lately so I have gone ahead and
committed a few changes towards an event-based solution to CVS.

In particular, there is a new 'handicap' trigger which usually
executes right before a game starts, and the 'createunit' event
now allows placing units at arbitrary locations on the map.

I'll play around with this some next week, and assuming it
works as planned, I'll release a new snapshot with one or more
maps converted to the new system after that.

Suggestions on what to change for a particular map are welcome,
and of course everyone is encouraged to update their own maps
themselves.

Jens