Recent Xconq checkins

[Stan Shebs]

The current pile of checkins includes the removal of two properties
of advances - "char" and "occurrence".  These were neither used nor
useful, so nobody should miss them.

Help for unit types now provides info about terrain effects on
productivity (how did that one get overlooked...).

The trident image set for civ2.g has had some problems fixed, as
well as the computation of shrunken images (no more fuchsia stripes!)

Finally, I've tweaked and added to the geographical features on
the big world maps.  Still need to figure out how to play an actual
game on them though... :-)

The supply algorithm in supply.c seems not to work, at least not in
the test/supply.g game which was supposed to demonstrate it.  It's
somewhat self-contained, so it's not clear to me why it would have
stopped working.

Stan