Freeciv

Patch depends on #602.

Decided to make this a MaxNumTiles requirement at Continent range, since that seems more likely to be extendable to other ranges (e.g. city). I didn't see much use for a continent size requirement at c/adjacent ranges ("are we on a small island or next to a small lake?"); maybe a little more if we were to make those work differently from normal and exclude the continent of the tile itself (just "are we next to a small lake?"), but even that didn't seem too useful. If it turns out we do want something like that, we can always add it later.

I just realized we can use this for another part of #588, i.e. for something needed now rather than something possibly useful in the future: The "ocean tile with at most two other adjacent ocean tiles" (bay) part. So I changed the name of the requirement type to "MaxRegionTiles", i.e. "at most this many tiles of the same region as the target tile" so we can make it do that at C/Adjacent ranges.

Updated patch; mainly pulling forward some changes I made for #652 (i.e. doing things right the first time).

Rebased patch on top of #696 (and #616)