add pickup_thrown option (trunk only)

add pickup_thrown option (trunk only)

     This patch by <email deleted> was released
when 3.4.1 was current and has been incorporated into slash'em.  It is
extremely useful while using ranged weapons.  When both autopickup and
pickup_thrown are enabled, walking across previously thrown objects will
pick them up even if they don't match the current pickup_types list.
[See cvs log for patchlevel.h for longer description.]