Ruleset capabilities for !ruleset_locked scenarios to use
Add ruleset capabilities. !ruleset_locked scenarios can be loaded only to those rulesets that fulfill capabilities requirements of the scenario.
I used to think that we do much better system than this, and temporary solution like this would only complicate things in the end. Now there is no full "scan scenario and ruleset for compatibility" -feature in sight, so this is better than nothing, no matter how much space it leaves for human error on how ruleset and scenario capabilities are defined.
We should maintain definition of some default capabilities. This patch already gives "minimum-default-sets" to classic, civ2civ3, experimental, multiplayer, sandbox, civ2, and webperimental. It's not given to civ1, alien, or stub. Exact list of units and terrains and other objects compatible ruleset must provide (and compatible scenario must limit itself to) is to be defined and documented (in the wiki?)