Touch ups to mon-spll.h, spl-data.h

Touch ups to mon-spll.h, spl-data.h

 * Buff test spawners. Specifically, make them get a wider, stronger
   range of summons without having to remember to tell arena to use
   pure-random place settings, through Plane Rend, and put the cloning
   code under a bit more visible pressure by giving them Phantom Mirror.
 * Cut the unused (and unusable) naga enchanter set.
 * Lower a hidden flavour number and properly tab a new entry in spl-data