civ2civ3 ruleset civilian units cause no ZoC

Patch by David Fernandez <bardo>

See patch #4816


git-svn-id: svn://svn.gna.org/svn/freeciv/trunk@25611 a0f10bec-cc02-0410-94fc-a9cfff90b4cd
Autosettlers calculate tile improvement value differently depending on
whether tile is currently being worked by the city or not.
For already worked tiles, we look for greatest delta (improvement to
city). For future tiles we look for having greatest total output from
the tile we're going to work next.

Needs to improvements in this area reported by Jacob Nevins <jtn>

See bug #21437


git-svn-id: svn://svn.gna.org/svn/freeciv/trunk@25612 a0f10bec-cc02-0410-94fc-a9cfff90b4cd