fix github issue #1029 - erroneous death feedback

for monsters that haven't died, when being removed from play to keep
them out of bones.

Reported by copperwater:  if the quest nemesis was present on a level
being saved as bones, it was removed from the map to keep it out of
the bones level but the quest feedback for nemesis death was given
in the process.  Would happen for blessed genocide of "*" too.  (It
didn't happen for #wizmakemap and I'm not sure why.)

This was an unintended side-effect of moving some common stuff from
mondead() and mongone() into m_detach().  The quest feedback isn't
actually common to both.  Instead of moving that back, pass a flag
that m_detach() can use to determine which routine called it.

Fixes #1029

doc/fixes3-7-0.txt

@@ -1584,6 +1584,8 @@ the fuzzer could get stuck in a loop if hero died in a way where life-saving
 	where life-saving teleports you out of it; if the level is full, the
 	teleport will fail and you'll immediately burn up again)
 fix unicorn horn's ability to repair blindness
+quest nemesis and a few other special monsters are suppressed from bones;
+	their death feedback could be given when they were removed
 
 
 Fixes to 3.7.0-x Platform and/or Interface Problems Exposed Via git Repository