Correct the rulesets civ1 and civ2

[sveinung]

"Airliftable" flag in civ1 should be removed from [unitclass_land]. Can never be done because the effect Airlift is never set but AGH hasn't figured this out (and probably shouldn't need to).

Fixed as a part of Bug #850673 after cazfi discovered that 2.6, not covered by my original patch, had this problem too.

[sveinung]

Civ 2: What should boarding and disembarking ships do to the movement points of land units? See bug #23782

I have improved civ1 and civ2 dis/embark move cost fidelity for Freeciv 3.1. I probably got the details wrong. Follow up patches with fine tuning would be great.

The new rules: Alighting to or boarding from a city or other transport at the same tile is free. The civ1 ruleset takes all movement when disembarking from a transport to an adjacent tile. Both civ1 and civ2 takes all movement when embarking to a transport from an adjacent tile. Embarking to a transport at an adjacent tile is legal for both.

Update: The civ1 rules. The civ2 rules.

"Transport Disembark 2" action is here already. If a "Transport Embark 2" helps civ1 or civ2 fidelity please request it before the 3.1 data file format freeze.