fix github issue #542 - clumsy "it" message

when encountering a hiding monster that's still unseen after being
revealed (so most likely invisible when hero lacks see invisible).
Change
|Wait!  There's an it hiding under <an object>!
to
!Wait!  There's something hiding under <an object>!
when hero tries to move onto the object.

Also, when a hidden monster reveals itself by attacking, change
|It was hidden under <an object>!
usually followed by "It hits." or "It misses."
to
|Something was hidden under <an object>!
without changing whatever follows.

Fixes #542

doc/fixes37.0

@@ -1,4 +1,4 @@
-NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.581 $ $NHDT-Date: 1625277130 2021/07/03 01:52:10 $
+NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.584 $ $NHDT-Date: 1625446012 2021/07/05 00:46:52 $
 
 General Fixes and Modified Features
 -----------------------------------
@@ -556,6 +556,8 @@ perm_invent: when buying shop goods using itemized purchasing while persistent
 change getloc fastmove keys in number_pad mode from hardcoded HJKL to the
 	run/rush movement keys (meta+number)
 allow using rush/run prefix key in getloc to fastmove the cursor
+avoid "it" in messages "Wait!  There's an it hiding under <an object>!" (hero
+	moving) and "It was hidden under <an object>!" (unseen monster moving)
 
 
 Fixes to 3.7.0-x Problems that Were Exposed Via git Repository

src/mhitu.c

@@ -1,4 +1,4 @@
-/* NetHack 3.7	mhitu.c	$NHDT-Date: 1606473488 2020/11/27 10:38:08 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.196 $ */
+/* NetHack 3.7	mhitu.c	$NHDT-Date: 1625446012 2021/07/05 00:46:52 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.245 $ */
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /*-Copyright (c) Robert Patrick Rankin, 2012. */
 /* NetHack may be freely redistributed.  See license for details. */
@@ -967,9 +967,10 @@ hitmu(register struct monst *mtmp, register struct attack *mattk)
      */
     if (mtmp->mundetected && (hides_under(mdat) || mdat->mlet == S_EEL)) {
         mtmp->mundetected = 0;
-        if (!(Blind ? Blind_telepat : Unblind_telepat)) {
+        if (!tp_sensemon(mtmp) && !Detect_monsters) {
             struct obj *obj;
             const char *what;
+            char Amonbuf[BUFSZ];
 
             if ((obj = g.level.objects[mtmp->mx][mtmp->my]) != 0) {
                 if (Blind && !obj->dknown)
@@ -979,7 +980,11 @@ hitmu(register struct monst *mtmp, register struct attack *mattk)
                 else
                     what = doname(obj);
 
-                pline("%s was hidden under %s!", Amonnam(mtmp), what);
+                Strcpy(Amonbuf, Amonnam(mtmp));
+                /* mtmp might be invisible with hero unable to see same */
+                if (!strcmp(Amonbuf, "It")) /* note: not strcmpi() */
+                    Strcpy(Amonbuf, Something);
+                pline("%s was hidden under %s!", Amonbuf, what);
             }
             newsym(mtmp->mx, mtmp->my);
         }

src/uhitm.c

@@ -1,4 +1,4 @@
-/* NetHack 3.7	uhitm.c	$NHDT-Date: 1617035737 2021/03/29 16:35:37 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.300 $ */
+/* NetHack 3.7	uhitm.c	$NHDT-Date: 1625446013 2021/07/05 00:46:53 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.311 $ */
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /*-Copyright (c) Robert Patrick Rankin, 2012. */
 /* NetHack may be freely redistributed.  See license for details. */
@@ -202,17 +202,24 @@ attack_checks(struct monst *mtmp,
             seemimic(mtmp);
             return FALSE;
         }
-        if (!((Blind ? Blind_telepat : Unblind_telepat) || Detect_monsters)) {
+        if (!tp_sensemon(mtmp) && !Detect_monsters) {
             struct obj *obj;
+            char lmonbuf[BUFSZ];
+            boolean notseen;
 
+            Strcpy(lmonbuf, l_monnam(mtmp));
+            /* might be unseen if invisible and hero can't see invisible */
+            notseen = !strcmp(lmonbuf, "it"); /* note: not strcmpi() */
             if (!Blind && Hallucination)
-                pline("A %s %s appeared!",
+                pline("A %s %s %s!", mtmp->mtame ? "tame" : "wild",
-                      mtmp->mtame ? "tame" : "wild", l_monnam(mtmp));
+                      notseen ? "creature" : (const char *) lmonbuf,
+                      notseen ? "is present" : "appears");
             else if (Blind || (is_pool(mtmp->mx, mtmp->my) && !Underwater))
                 pline("Wait!  There's a hidden monster there!");
             else if ((obj = g.level.objects[mtmp->mx][mtmp->my]) != 0)
                 pline("Wait!  There's %s hiding under %s!",
-                      an(l_monnam(mtmp)), doname(obj));
+                      notseen ? something : (const char *) an(lmonbuf),
+                      doname(obj));
             return TRUE;
         }
     }