fix github issue #196 - green slime feedback

Fixes #196

If you didn't die from turning into green slime but then died because
green slimes had been genocided, the message given assumed that you
had just seen "OK, you don't die" from answering No to "Really die?".
Its wording didn't make sense if the reason you didn't die was an
amulet of life-saving.  Give a different message for that case.

Also, if you survive turning into slime (via either method) and either
green slimes are still around or you answer No to "Really die?" when
they've been genocided, give a message after "You survived that attempt
on your life" pointing out that you have done so in green slime form.
Useful since prior to 3.6.2 you would have reverted to original form--
despite the Slimed countdown saying you had turned into green slime.

src/polyself.c

@@ -1,4 +1,4 @@
-/* NetHack 3.6	polyself.c	$NHDT-Date: 1556497911 2019/04/29 00:31:51 $  $NHDT-Branch: NetHack-3.6.2-beta01 $:$NHDT-Revision: 1.132 $ */
+/* NetHack 3.6	polyself.c	$NHDT-Date: 1559664952 2019/06/04 16:15:52 $  $NHDT-Branch: NetHack-3.6 $:$NHDT-Revision: 1.133 $ */
 /*      Copyright (C) 1987, 1988, 1989 by Ken Arromdee */
 /* NetHack may be freely redistributed.  See license for details. */
 
@@ -163,7 +163,7 @@ polyman(fmt, arg)
 const char *fmt, *arg;
 {
     boolean sticky = (sticks(youmonst.data) && u.ustuck && !u.uswallow),
-            was_mimicking = (U_AP_TYPE == M_AP_OBJECT);
+            was_mimicking = (U_AP_TYPE != M_AP_NOTHING);
     boolean was_blind = !!Blind;
 
     if (Upolyd) {
@@ -186,6 +186,7 @@ const char *fmt, *arg;
         if (multi < 0)
             unmul("");
         youmonst.m_ap_type = M_AP_NOTHING;
+        youmonst.mappearance = 0;
     }
 
     newsym(u.ux, u.uy);
@@ -633,6 +634,7 @@ int mntmp;
     if (mons[mntmp].mlet != S_MIMIC) {
         /* as in polyman() */
         youmonst.m_ap_type = M_AP_NOTHING;
+        youmonst.mappearance = 0;
     }
     if (is_male(&mons[mntmp])) {
         if (flags.female)