road under halt (r11091)

[Andarix]

It is possible that public roads under player halt can be built over by other players.

This means that the player can no longer build over his own halt.



There is currently a contradiction that streets can be built under other players' halts, but not halts on other player streets.

[Roboron]

Looking at the code, there's no check for halts when building a road (there's a check for buildings, but apparently doesn't apply to halts).

I see many possible ways to solve this:

1) If a player build a halt over a public road, then the road will change its ownership to the player.
2) Player A can't build roads under Player B halts.
3) Player A can build roads under Player B halts, but the road will keep its current ownership.
4) Player A can build roads under Player B halts, but player B can still improve its existing halts on Player A road.

I applied solution #2 on r11099, but you may discuss if you prefer another one.

I also added a warning when you are trying to build a way over an invalid building.

[Andarix]

I would generally be in favor of all streets in cities becoming public streets. The reason is trams. The rails cannot be built on foreign roads, which makes them difficult or even impossible to use.

Another reason is stops. Foreign player streets prevent city areas from being covered.