& btsetxy()
 
  Syntax: btsetxy(<UnitDB>,<MapDB>,<x>,<y>[,<z>])
 
  This function sets the position of <UnitDB> to hex <x>,<y> and 
  optionally at an altitude of <z>.
 
  If the argument <z> is omitted, the function determines the 
  elevation of the hex <x>,<y> and sets <z> to that value.
 
	Note: In that the function automatically ascertains the value of z, 
	it is generally wisest to omit this argument.
 
  The function returns 1 if successful.
 
  Error Messages:
 
  * If <UnitDB> is not a valid RS unit the function returns #-1 
     INVALID TARGET
  * If <MapDB> is not a valid map object the function returns #-1 
    INVALID MAP
  * If <x> is outside the boundaries of the map the function returns 
    #-1 X COORD
  * If <y> is outside the boundaries of the map the function returns 
    #-1 Y COORD
  * If <z> is > 10000 the function returns #-1 Z COORD 
 
  Example:
  Given that #1234 is a mech and #62 is a map object
 
  > think btsetxy(#1234,#62,10,10,0)
  1