(svn r7299) -CodeChange: Train and Aircraft Build window GUI code simplified a bit:

- using one engine list instead of 3
- removed engine filters (loco, wagons, helicopters, etc.)
- EngineList code isolated from GUI (moved to helpers.cpp - reusing CBlobT code which does exactly what is needed for EngineList)
- removed unnecessary  "optimization" (rebuild and sort engine list on each WE_PAINT)

openttd.h

@@ -55,6 +55,7 @@ typedef uint32 CursorID;
 typedef uint16 EngineID;
 typedef uint16 UnitID;
 typedef uint16 StringID;
+typedef EngineID *EngineList; ///< engine list type placeholder acceptable for C code (see helpers.cpp)
 
 /* IDs used in Pools */
 typedef uint16 VehicleID;