Allow dropping just picked up items

When using a menu to drop or put in items into a container,
allow putting in the item (or items) you picked up previously,
by selecting the 'P' entry from the item class menu

Inspired by the itemcat patch by Stanislav Traykov.

Invalidates saves and bones.

include/obj.h

@@ -117,7 +117,8 @@ struct obj {
     Bitfield(cknown, 1); /* for containers (including statues): the contents
                           * are known; also applicable to tins */
     Bitfield(lknown, 1); /* locked/unlocked status is known */
-    /* 4 free bits */
+    Bitfield(pickup_prev, 1); /* was picked up previously */
+    /* 3 free bits */
 
     int corpsenm;         /* type of corpse is mons[corpsenm] */
 #define leashmon corpsenm /* gets m_id of attached pet */