Most (i.e. 13 of 15) callers of GetNewVehiclePos() do not care for the return and the others can figure it out by inspecting the information returned in struct GetNewVehiclePosResult.
Therefore remove the return value.
-The user will notice the following changes:
All vehicle types behaves in the same way
Adding/removing an engine (new design and so on) can no longer result in the window selecting a new engine
All valid replacements will be displayed since it looks at refitting options as well (this solves the missing ships with the newships GRF)
Since you can't replace an engine into itself, the engine selected in the left list will no longer appear in the right list
-The code changes:
Instead of looping all engines all the time, each list generates a list like the build windows
This ensures consistent list generation since only one function can loop all engines
Unified code for all vehicle types
It now use the lists to call the drawing code in the build vehicle window
Works on selected EngineIDs instead of selected index in the list
-Codechange: CheckCompatibleRail() is only called for tiles which are known to contain a piece of rail. Simplify the function accordingly by eliminating unnecessary checks.
-Fix (?): Also fix an inconsistency in deciding what a compatible rail type is between level crossings and other rail tiles. It is unknown if this caused any problems.
Change the signature of Swap() to be less error prone, i.e. pass the variables to be swapped by reference instead of passing pointers to the variables.
Just do Swap(x, y) instead of Swap(&x, &y). This prevents accidents when the variables are pointers.
