Gamesetup should have a clean way to reset map settings

[serveurix]

Go in the match setup screen. Choose "Scenario" > a circular map like "Battle for the Tiber". Than select an other map in scenarios, square this time, like "Fast Oasis". Launch the match.

​http://pix.toile-libre.org/upload/original/1410803422.png

Congratulations, your square map is now round ! \o/

Reveal the map via the dev overlay, for fun :

​http://pix.toile-libre.org/upload/original/1410803491.png

Your unusable civ center has disappeared ! \o/ You can make it reappear at any time by reactivating the fog of war. But you can't destroy it, it is in the fog of war. _o_ You've got to wait for an enemy to liberate you. Or resign.

[mimo]

In 15757:

reset some map attribute, addresses #2803

[mimo]

The problem was analogous to #2793. Some maps do not define some settings (usually because they use the default), but these are not reset in gamesetup.js. The problem is that the settings object contains settings defined at different level and there is no way to know which ones have been set by the previous maps. In this fix and the one from #2793, the faulty settings have been reset by hand, but we should have a way to determine which one have to be reset.

[mimo]

In 16278:

fix initialization when changing maps, refs #2803

[elexis]

Same as #3883

[elexis]

Closing as duplicate of #2803 since that contains a bit more information/desparation.