(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()

variables.h

@@ -431,6 +431,9 @@ VARDEF SignStruct *_new_sign_struct;
 /* tunnelbridge */
 #define MAX_BRIDGES 13
 
+/* Autoreplace vehicle stuff*/
+VARDEF byte _autoreplace_array[255];
+
 /* Debugging levels */
 VARDEF int _debug_spritecache_level;
 VARDEF int _debug_misc_level;