improve messaging on vampire bat to fog cloud transition in Vlad's

improve messaging on vampire bat to fog cloud transition in Vlad's

Bug 271 - #H4167: vampires being fog clouds show up as bats on telepathy

A bug reporter wrote:
> In top level of Vlad's, the vampires hiding as fog clouds in the closets show
> up on telepathy as B, when far-looked as vampire bat.  once the door opens they
> are fog clouds.
>
> I currently have telepathy from the PYEC.

The vampire /was/ shapeshifted into a vampire bat, but once the secret door
was revealed, it shifted into a fog cloud in order to pass under the door.

If you were to blast the door with a wand of striking from a distance,
you would have encountered the vampire bat.

This clarifies the situation through better messaging.

--------
Original debug call stack trace:
     NetHack.exe!newcham(monst * mtmp, permonst * mdat, char polyspot, char msg) Line 3140
     NetHack.exe!vamp_shift(monst * mon, permonst * ptr) Line 1598
     NetHack.exe!m_move(monst * mtmp, int after) Line 1219
     NetHack.exe!dochug(monst * mtmp) Line 566
     NetHack.exe!dochugw(monst * mtmp) Line 100
     NetHack.exe!movemon(...) Line 707
     NetHack.exe!moveloop(char resuming) Line 105
     NetHack.exe!main(int argc, char * * argv) Line 105