msummon,nasty result counts (trunk only)

msummon,nasty result counts (trunk only)

     Reported in Dec'04 by <email deleted>, the
monster spell "summon nasties" could mistakenly give a message of "a
monster appears" instead of "monsters appear" when more that one monster
gets summoned.  Some of the candidate monsters for nasty() can produce a
group from makemon(), as can ones for msummon() which nasty() sometimes
calls in Gehennom.  Compare the number of monsters before and after the
creation attempt(s) instead of assuming makemon() creates one at a time.

     I don't know whether other routines face the same mis-count issue,
but I suspect there may be several.