(svn r1323) Adding autoreplace feature

This feature works much like autorenew, but it will get you a new engine type instead of a new one of the same type. Once 
ordered, it will automatically replace the engines while they visits a depot. The GUI for setting this up have been added on the 
vehicle overview windows
Note: autorenew is now autoreplace, but to the same engine type
Nice new features, that was added to make this possible
- windows can now have two independant vertical scrollbars
- CMD_SHOW_NO_ERROR have been added as a flag for DoCommandP. It will make it do the action instead of showing the red box with 
estimated costs even if shift is pressed
- fixed problem where enginetypes where not initialized when loading a game. It's now done in InitializeGame()

gui.h

@@ -85,6 +85,7 @@ void CheckRedrawStationCoverage(Window *w);
 void ShowSmallMap();
 void ShowExtraViewPortWindow();
 void SetVScrollCount(Window *w, int num);
+void SetVScroll2Count(Window *w, int num);
 void SetHScrollCount(Window *w, int num);
 int HandleEditBoxKey(Window *w, int wid, WindowEvent *we);