(svn r3396) - Autoreplace changes:

- Change fixed array per player to a single pool. This avoids future problems
    with vehicle numbers and decreases savegame size. Engine replacements from
    previous savegames will be lost.
  - Move engine replacement code from players.c to engine.c.
                                      (thanks to blathijs for rewriting this)

saveload.h

@@ -47,7 +47,8 @@ typedef enum SLRefType {
 	REF_STATION     = 2,
 	REF_TOWN        = 3,
 	REF_VEHICLE_OLD = 4,
-	REF_ROADSTOPS   = 5
+	REF_ROADSTOPS   = 5,
+	REF_ENGINE_RENEWS = 6,
 } SLRefType;