fix #H239 - doppleganger/mimic bug

From a bug report:  a shapechanger
which becomes a mimic would always stay as 'm' rather than take on object
or furniture shape.  Same applied to monsters which hide in other ways.
The code did that deliberately, but I don't think that it's actually
necessary so this lets them mimic/hide when they're in the right shape.
If they change form to non-mimic/hider while concealed, concealment ends.

     It would be fun to have shapechangers-as-mimics actually change their
mimicked shapes periodically, but this doesn't do that.  They'd probably
change to non-mimic quicker than they'd mimic something else so it's not
worth the effort.

doc/fixes34.4

@@ -311,6 +311,7 @@ fireproof, non-rustable weapon would be revealed as fireproof by hitting a
 	rust-causing target; ditto for fixed crysknife
 surviving choking while eating various foods (cockatrice egg, fortune cookie,
 	wolfsbane, others) didn't carry through to those foods' side-effects
+shapechangers who take on mimic or hider form will mimic or hide when feasible
 
 
 Platform- and/or Interface-Specific Fixes

src/mon.c

@@ -1,4 +1,4 @@
-/*	SCCS Id: @(#)mon.c	3.5	2007/01/12	*/
+/*	SCCS Id: @(#)mon.c	3.5	2007/02/08	*/
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /* NetHack may be freely redistributed.  See license for details. */
 
@@ -2395,7 +2395,7 @@ register struct monst *mtmp;
 {
 	struct trap *t;
 
-	if((mtmp->cham >= LOW_PM) || mtmp->mcan || mtmp->m_ap_type ||
+	if (mtmp->mcan || mtmp->m_ap_type ||
 	   cansee(mtmp->mx, mtmp->my) || rn2(3) || (mtmp == u.ustuck) ||
 	   /* can't hide while trapped except in pits */
 	   (mtmp->mtrapped && (t = t_at(mtmp->mx, mtmp->my)) != 0 &&
@@ -2646,6 +2646,8 @@ boolean msg;		/* "The oldmon turns into a newmon!" */
 		wormgone(mtmp);
 		place_monster(mtmp, mtmp->mx, mtmp->my);
 	}
+	if (mtmp->m_ap_type && mdat->mlet != S_MIMIC)
+	    seemimic(mtmp);	/* revert to normal monster */
 
 	/* (this code used to try to adjust the monster's health based on
 	   a normal one of its type but there are too many special cases