Add 'pickup_stolen' option

Add pickup_stolen option to autopick items stolen from you by a nymph or
monkey, even if they don't match your normal autopickup settings.
Replace was_dropped, was_thrown with a 2-bit bitfield that can contain
values LOST_DROPPED, LOST_THROWN, and LOST_STOLEN (or 0), since they
should all be mutually exclusive anyway as they track the most recent
way the item left the hero's inventory.

[Rebase/merge conflict fixed up.  PR]

include/obj.h

@@ -124,10 +124,9 @@ struct obj {
 #define on_ice recharged    /* corpse on ice */
     Bitfield(lamplit, 1);   /* a light-source -- can be lit */
     Bitfield(globby, 1);    /* combines with like types on adjacent squares */
-    Bitfield(greased, 1);    /* covered with grease */
-    Bitfield(nomerge, 1);    /* set temporarily to prevent merging */
-    Bitfield(was_thrown, 1); /* thrown by hero since last picked up */
-    Bitfield(was_dropped, 1); /* dropped deliberately by the hero */
+    Bitfield(greased, 1);   /* covered with grease */
+    Bitfield(nomerge, 1);   /* set temporarily to prevent merging */
+    Bitfield(how_lost, 2);  /* stolen by mon or thrown, dropped by hero */
 
     Bitfield(in_use, 1); /* for magic items before useup items */
     Bitfield(bypass, 1); /* mark this as an object to be skipped by bhito() */
@@ -459,6 +458,12 @@ struct obj {
 #define POTHIT_MONST_THROW 2 /* thrown by a monster */
 #define POTHIT_OTHER_THROW 3 /* propelled by some other means [scatter()] */
 
+/* tracking how an item left your inventory */
+#define LOST_NONE    0 /* still in inventory, or method not covered below */
+#define LOST_THROWN  1 /* thrown or fired by the hero */
+#define LOST_DROPPED 2 /* dropped or tipped out of a container by the hero */
+#define LOST_STOLEN  3 /* stolen from hero's inventory by a monster */
+
 /*
  *  Notes for adding new oextra structures:
  *