fix #H6338 - naming mimicked potion

Player tried to #name a potion on the floor and got prompted to call a
stream of fluid (sink feedback) instead of a potion.  A mimic posing
as an object is represented by a partially initialized object when
examining its map location.  #name for floor object uses the same data
as look_at.

obj->fromsink overloads obj->corpsenm which is set to NON_PM (-1) even
when creating a non-init'd object.  'fromsink' was only being forced to
0 when creating an init'd object (unlike leash which has its overload
of corpsenm set properly regardless of caller's request to init).  So
docall() treated a mimicked potion as a sink stream.

The fix is straightforward but has pointed out another bug which is
harder to fix.  Examining a floor object next to you sets that obj's
dknown flag as if you had seen it up close (a new feature in 3.6.0).
But a mimicked item is discarded as soon as it's been looked at, so
looking again from a non-adjacent spot will give different feedback
since the previously set dknown will be unset when replaced by a new
fake object.  So you can use '/' and ';' to recognize mimics without
provoking them into motion.  Best fix:  mimicking an object should use
a fully initialized one which is tracked via monst->mextra, but that
will break save file compatibility.  Possible hack:  change monst->
mappearance into a mask which uses N bits for object type (instead of
full 'int') and one of the other bits to track obj->dknown.  Examining
an adjacent object probably ought to set bknown for priests, so bknown
and blessed/uncursed/cursed would need to be tracked too.

doc/fixes36.1

@@ -464,6 +464,8 @@ improve #adjust command's handling of the '$' and '#' inventory slots
 prevent #adjust from allowing anything to be moved into the special '-' slot
 sometimes rings dropped into sinks can be found in the pipes
 doors in special levels were always generated in vertical orientation
+assigning a type name to a potion on the floor which is actually a mimic could
+	prompt "Call a stream of <potion-type> fluid:" (bogus 'fromsink')
 
 
 Fixes to Post-3.6.0 Problems that Were Exposed Via git Repository