Discovered while testing the from-what enhancements to enlightenment.
Polymorphing into a vampire confers the ability to sense humans and
elves without having telepathy or being triggered by blindness. That
would be taken away if you polymorphed into something else, but was
being left in effect if polymorph just timed out and hero returned to
normal form.
Same thing occurred for sensing shriekers if you poly'd into a purple
worm and then reverted to normal (something much less likely to get
noticed and not really subject to abuse if it ever did).
Bonus fix: the code involved was using 0 to mean that Warn_of_mon
from polymorph wasn't in effect, but 0 is also giant ant. This makes
it use NON_PM for that instead.
67826ff67b