B01003 - blindfold vs dust vortex

This started out as a change to address the strange sequence of messages if
you remove a blindfold while engulfed in a dust vortex.  That is addressed
by a new function that can be called in such situations.  Calls to this
function were added in all the cases where the can_blnd() engulfing
conditions end as a result of player action.  There are some other cases
that end ucreamed or usleep, but they happen between turns and shouldn't
need extra handling.

While I was at it, I noticed that a unicorn horn or prayer would cure
blindness even while engulfed in a dust vortex.  This is useless, because
you immediately get blind again the next turn.  So, I added checks to avoid
doing this.  Finally, it didn't make sense for eating a carrot to cure your
blindness in these situations either, only for it to return immediately.

src/do.c

@@ -1580,8 +1580,10 @@ wipeoff()
 	if (!Blinded) {
 		pline("You've got the glop off.");
 		u.ucreamed = 0;
-		Blinded = 1;
-		make_blinded(0L,TRUE);
+		if (!gulp_blnd_check()) {
+		    Blinded = 1;
+		    make_blinded(0L,TRUE);
+		}
 		return(0);
 	} else if (!u.ucreamed) {
 		Your("%s feels clean now.", body_part(FACE));