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.

src/allmain.c

@@ -57,6 +57,7 @@ moveloop_preamble(boolean resuming)
     if (!resuming) { /* new game */
         g.context.rndencode = rnd(9000);
         set_wear((struct obj *) 0); /* for side-effects of starting gear */
+        reset_justpicked(g.invent);
         (void) pickup(1);      /* autopickup at initial location */
         /* only matters if someday a character is able to start with
            clairvoyance (wizard with cornuthaum perhaps?); without this,