Freeciv-3.2 updates to tileset format

[cazfi]

This is meant to be a bit similar thread to what we have about ruleset changes on the ruleset forum. Tileset format just usually changes much much less than ruleset format. There actually has been no thread like this at all for freeciv-3.1.

I'm currently working on finally implementing support for city style specific citizen sprites. The ruleset format has had field for them since 2003, but they have never been actually implemented on the client side! hrm #683532

[cazfi]

Unit main sprite (not just the activity icon) can now depend on unit's current activity. osdn #46387

Note that, unlike with activity icons, there's no way to distinguish between activity targets with unit main sprite, so "Road" activity will have the same sprite regardless of exact type of the road (e.g. "Road", "Railroad", "Maglev")