fix github issue #1413 - mimic feedback for gold

Issue reported by ars3niy:  if a mimic was given the shape of a
gold piece it gets reported as 2 gold pieces but the message was
|A gold pieces appears next to you.

Avoid article "A" prefix, and use plural verb "appear" instead of
singular "appears", yielding
|Gold pieces appear next to you.

Fixes #1413

doc/fixes3-7-0.txt

@@ -2116,6 +2116,7 @@ successfully disarming a chest trap was clearing the chest's 'tknown' bit
 	used up the trap
 when game ended with 'force_invmenu' On, final disclosure of inventory would
 	contain spurious menu entry "? - (list likely candidates)"
+avoid reporting "a gold pieces appears next to you" for mimic
 
 
 Fixes to 3.7.0-x Platform and/or Interface Problems Exposed Via git Repository

src/makemon.c

@@ -1485,8 +1485,10 @@ makemon(
             }
             if (what) {
                 set_msg_xy(mtmp->mx, mtmp->my);
-                Norep("%s%s appears%s%c", what,
+                Norep("%s%s %s%s%c", what,
                       exclaim ? " suddenly" : "",
+                      /* 'what' might be "gold pieces" so need plural verb */
+                      vtense(what, "appear"),
                       next2u(x, y) ? " next to you"
                       : (distu(x, y) <= (BOLT_LIM * BOLT_LIM)) ? " close by"
                         : "",

src/pager.c

@@ -220,7 +220,7 @@ mhidden_description(
             what = (otmp && otmp->otyp != STRANGE_OBJECT)
                    ? simpleonames(otmp)
                    : obj_descr[STRANGE_OBJECT].oc_name;
-            if (incl_article)
+            if (incl_article && (!otmp || otmp->quan == 1L))
                 what = an(what);
             Strcat(outbuf, what);