fix #Q117 - vomiting by rodents & more

fix #Q117 - vomiting by rodents & more

     From a bug report:  you could vomit when polymorphed into a rat but real life
rats can't/don't vomit.  The latter was confirmed by <Someone> and <Someone>.
While testing a fix for this, I discovered a couple of other problems.
Healing magic which cured sickness failed to heal Vomiting (potion or
spell; unicorn horn deals with them separately).  Enlightenment failed to
report Vomiting (it's not shown on the status line).  Most significant was
that vomiting_dialogue() called vomit() twice (also make_confused() and
make_stunned() three times for every once intended).  It was dividing the
remaining turns by 3 and then using that value to decide what to do, but
only message display took into account that the same divided value would
occur on 3 consecutive turns (or just 2 for the final countdown to 0,
because dialog routine gets called before timed-property decrement).