<foo> suddenly appears next to you (trunk only)

<foo> suddenly appears next to you (trunk only)

     Give demon lords and other monsters who teleport to your location a
oneshot arrival message.  Brought about by the report of the late "<demon>
appears" message delivered during its bribery demand, after the character
had already been able to see it for long enough to extract gold from a bag.
Now, if you can't see or sense a monster before it teleports to you, and
you can see or sense it after, you'll get "<monster> suddenly appears!".
The message will be given at most once for any given monster, and it won't
be shown at all if you already see/sense the monster before it teleports or
still don't see/sense it afterwards.  The fixes entry is deliberately a bit
vague (and I put it in the new feature section rather than the fix section).

     The change from long to unsigned long for monst.mstrategy may bring
some lint complaints along with it.  The various constants (STRAT_xxx) used
to populate it are still signed.  I didn't increment EDITLEVEL for this;
existing data should still work ok.