(svn r1786) -Fix: unitnumber is increased to 16bit, so now you can have up to 5000

trains in one game (instead of the 240 which was the current value). 
Default max allowed vehicles per type is changed:
  Trains:  500 (old 80)
  Road:    500 (old 80)
  Ships:   200 (old 40)
  Aicraft: 300 (old 50)
(Tnx to Celestar and Darkvater for checking the patch)

variables.h

@@ -11,6 +11,8 @@
 # define MAX_PATH 260
 #endif
 
+typedef uint16 UnitID;   //! All unitnumber stuff is of this type (or anyway, should be)
+
 // Prices and also the fractional part.
 VARDEF Prices _price;
 VARDEF uint16 _price_frac[NUM_PRICES];
@@ -135,10 +137,10 @@ typedef struct Patches {
 	uint8 toolbar_pos;			// position of toolbars, 0=left, 1=center, 2=right
 	uint8 window_snap_radius; // Windows snap at each other if closer than this
 
-	byte max_trains;				//max trains in game per player (these are 8bit because the unitnumber field can't hold more)
-	byte max_roadveh;				//max trucks in game per player
-	byte max_aircraft;			//max planes in game per player
-	byte max_ships;					//max ships in game per player
+	UnitID max_trains;				//max trains in game per player (these are 16bit because the unitnumber field can't hold more)
+	UnitID max_roadveh;				//max trucks in game per player
+	UnitID max_aircraft;			//max planes in game per player
+	UnitID max_ships;					//max ships in game per player
 
 	bool servint_ispercent;	// service intervals are in percents
 	uint16 servint_trains;	// service interval for trains