(svn r21933) -Codechange: Split cur_order_index into cur_auto_order_index and cur_real_order_index to keep track of the current real order in an unambiguous way.
-Fix [FS#4440]: Automatic orders behave now stable wrt. service orders and are not added or removed depending on the need of servicing.
-Fix: Various other issues with automatic orders, e.g. vehicles getting stuck with "no orders" when there are automatic orders at the end of the order list.

(svn r18481) -Codechange: unify the curve pathfinder penalty defaults; 0.01 tile won't make a dent, 3 tiles might be a bit too much
-Feature-ish: make maximum pathfinder penalties for finding depots customisable, also increase it slightly to 20 tiles worth of penalties.

(svn r17897) -Fix [FS#3255]: CB15 and CB36 (capacity) were not always called when they should.
-Codechange: Move capacity calculation to a single function for all vehicle types, so the behaviour can be kept consistent easier.

(svn r15541) -Revert (r15399): 'v->cargo_type' is also used in other places, which cannot accept CT_INVALID.
-Codechange: Add Engine::GetDefaultCargoType() and Engine::CanCarryCargo() and use them.
-Fix [FS#2617]: When articulated parts have no available default cargo, use the cargo type of the first part for livery selection.
-Change: To decide whether a vehicle is refittable do not test its current capacity for being zero, but always use the 'capacity property'.
Note: The property is used unmodifed without calling CB 15/36. By setting it to a non-zero value and returning zero in the callback vehicles can be refitted to/from zero capacity for e.g. livery effects.
Note: It is intentional that you cannot control refittability by CB 36.