attack/damage by trapper and lurker above

Change trappers and lurkers above to remove digestion damage.  They
fold themselves around rather than swallow the victim.  There were
are lot of places that assumed that an engulfer which is an animal
would swallow and digest the victim.  In hindsight, it might have
been simpler to take the M1_ANIMAL flag off of trappers and lurkers
above.

This adds a new digests() predicate for creatures with AT_ENGL+AD_DGST
(purple worm) and also enfolds() for AT_ENGL+AD_WRAP (both 't'-class
critters).

There are several minor fixes mixed in with this.  I didn't record
them as I went along but the two I remember are
1) if poly'd into a holder and holding on to a monster, the '<' and
   '>' commands refursed to work; release the held creature first
   and then treat those commands as normal;
2) throwing a non-weapon while engulfed by an ochre jelly reported
   "the <item> vanishes into the ochre jelly's /currents/".

This needs a lot more testing.  I found and fixed multiple minor
details before my own testing burned out.

include/mondata.h

@@ -86,6 +86,8 @@
 #define is_wooden(ptr) ((ptr) == &mons[PM_WOOD_GOLEM])
 #define thick_skinned(ptr) (((ptr)->mflags1 & M1_THICK_HIDE) != 0L)
 #define hug_throttles(ptr) ((ptr) == &mons[PM_ROPE_GOLEM])
+#define digests(ptr) dmgtype_fromattack((ptr), AD_DGST, AT_ENGL) /* purple w*/
+#define enfolds(ptr) dmgtype_fromattack((ptr), AD_WRAP, AT_ENGL) /* 't' */
 #define slimeproof(ptr) \
     ((ptr) == &mons[PM_GREEN_SLIME] || flaming(ptr) || noncorporeal(ptr))
 #define lays_eggs(ptr) (((ptr)->mflags1 & M1_OVIPAROUS) != 0L)