The code to choose a likely target when applying a polearm was
basing its decision on visible spots which contained monsters,
so could expose the location of a hidden monster if there was
only one such spot within polearm range. Not mentioned in the
report: it also wouldn't pick remembered, unseen monster unless
there was a monster still at that spot.
I've changed it to choose candidate location based on the glyphs
shown rather than on the presence of monsters.
b17c6d0b54