vampires now shapeshift [trunk only]

- can shift into fog clouds, vampire bats, and vampire lords into wolves
- after being "killed" in shifted form, they transform back rather than get
  destroyed, and you must take them on in vampire form to defeat them
- can deliberately shift into fog clouds to pass under closed doors

src/cmd.c

@@ -464,7 +464,8 @@ domonability()
 	    if(u.uburied)
 		pline("Unfortunately sound does not carry well through rock.");
 	    else aggravate();
-	} else if (Upolyd)
+	} else if (youmonst.data->mlet == S_VAMPIRE) return dopoly();
+	else if (Upolyd)
 		pline("Any special ability you may have is purely reflexive.");
 	else You("don't have a special ability in your normal form!");
 	return 0;