fix #H8215 - monster intrinsics from worn gear

Fixes #177

The monst struct has 'mintrinsics' field which attempts to handle
both mon->data->mresists and extrinsics supplied by worn armor, but
polymorph/shape-change was clobbering the extrinsics side of things.
Potentially fixing that by changing newcham() to use set_mon_data(...,1)
instead of (...,0) solved that but exposed two other bugs.  Intrinsics
from the old form carried over to the new form along with extrinsics
from worn armor, and update_mon_intrinsics() for armor being destroyed
or dropped only worked as intended if the armor->owornmask was cleared
beforehand--some places were clearing it after, so extrinsics from worn
gear could persist even after that gear was gone.

So, fixing the set_mon_data() call in newcham() was a no go.  This
fixes update_mon_intrinsics() and adopts the suggested code from
github pull request #177 to have mon->mintrinsics only handle worn
gear instead of trying to overload innate intrinsics with that.  This
is a superset of that; the flag argument to set_mon_data() is gone
and mon->mintrinsics has been renamed mon->mextrinsics.  (The routine
update_mon_intrinsics() ought to be renamed too, but I didn't do that.)

src/polyself.c

@@ -1,4 +1,4 @@
-/* NetHack 3.6	polyself.c	$NHDT-Date: 1548208238 2019/01/23 01:50:38 $  $NHDT-Branch: NetHack-3.6.2-beta01 $:$NHDT-Revision: 1.126 $ */
+/* NetHack 3.6	polyself.c	$NHDT-Date: 1550524564 2019/02/18 21:16:04 $  $NHDT-Branch: NetHack-3.6.2-beta01 $:$NHDT-Revision: 1.127 $ */
 /*      Copyright (C) 1987, 1988, 1989 by Ken Arromdee */
 /* NetHack may be freely redistributed.  See license for details. */
 
@@ -43,7 +43,7 @@ set_uasmon()
     struct permonst *mdat = &mons[u.umonnum];
     int new_speed, old_speed = youmonst.data ? youmonst.data->mmove : 0;
 
-    set_mon_data(&youmonst, mdat, 0);
+    set_mon_data(&youmonst, mdat);
 
 #define PROPSET(PropIndx, ON)                          \
     do {                                               \