I used ^G to create a monster and specified "invisible owlbear". I
then got "An owlbear appears next to you." Except it didn't; it was
invisible and I lacked see-invisible. I imagine that newsym() was
called for the new-yet-invisible monster, but that remained buffered
and was gone overridden by the time pending map update got flushed
at some point after the monster was made invisible.
Add a new makemon() flag to turn a newly created monster invisible
during its creation, before "monster appears" message is delivered.
Since that message will now be suppressed in this situation, use the
cursor-flash hack that indicates where the new, unseen monster got
placed. Creating "1000 invisible <mon>" is something you probably
won't do twice.
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