fix #K4498 - stethoscope vs double trouble Wizard

When the Wizard is diguised as some other monster, applying a stethscope
described him as "that <foo> is really a <foo>".

doc/fixes5-0-1.txt

@@ -74,6 +74,9 @@ Some optimizations of the glyph lookup - don't produce names for swallow
 	glyph index in populate_glyphname_hash_indices; build a sorted
 	index for loadsyms so that it can be searched with bsearch
 	(pr #1612 by chasonr)
+stethoscope applied to one monster disguised as another (double-trouble Wizard)
+	mis-described undisguised form (unintended side-effect of 5.0 commit
+	064523e162f8e30bdb76186a854b9d8958f3b340)
 
 
 Platform- and/or Interface-Specific Fixes

src/apply.c

@@ -390,7 +390,10 @@ use_stethoscope(struct obj *obj)
     }
     if ((mtmp = m_at(rx, ry)) != 0) {
         const char *mnm = x_monnam(mtmp, ARTICLE_A, (const char *) 0,
-                                   SUPPRESS_IT | SUPPRESS_INVISIBLE, FALSE);
+                                   (SUPPRESS_IT | SUPPRESS_INVISIBLE
+                                    /* stethoscope reveals true form; seemimic
+                                       below will clear mtmp->mappearance */
+                                    | SUPPRESS_MAPPEARANCE), FALSE);
 
         /* gb.bhitpos needed by mstatusline() iff mtmp is a long worm */
         gb.bhitpos.x = rx, gb.bhitpos.y = ry;