(svn r11014) -Fix (r11011) [FS#1170]: crash when selling the first train of a consist.

(svn r11013) -Fix [FS#1171]: MoveGoodsToStation's search area is too small as it assumed a lower maximum catchment area than the real maximum catchment area. Based on a patch by PhilSophus.

(svn r11011) -Fix [FS#1129]: GetFirstVehicleInChain did change the game state while being marked const.
-Codechange: do not brute force determine the first vehicle in the chain or previous vehicle, but do it by properly accounting the previous and first pointers when updating the next pointer. This gives a performance increase of about 15% when there are a lot of vehicles in the game.

(svn r11009) -Codechange: unvirtualise IsValid as that isn't needed with templates. This gives up to 10% performance increase in games with lots of vehicles.

(svn r11006) -Fix: spectators are not allowed to issue commands. Issue spotted by SmatZ.

(svn r11005) -Codechange: move the tiletype specific terraforming checks to the functions for those tile types.
-Codechange: barren the rail grounds on terraforming.

(svn r11004) -Codechange: some reworks of the saveload mechanism to be able to save and load private and protected variables in the vehicle struct.

(svn r11003) -Codechange: replace Vehicle->next to Vehicle->Next() and Vehicle->SetNext() so we can trap instances that change a next pointer and (in the future) update the first/previous pointers based on that.

(svn r11002) -Codechange: unhackify the cargo packet list saving (a little).

(svn r11001) -Codechange: unify the way to determine whether a vehicle is in a depot.