These functions allow the current index into the history list to be
set or changed.
Function: inthistory_set_pos (int pos)
Set the position in the history list to pos, an absolute index
into the list.
Function: HIST_ENTRY*previous_history ()
Back up the current history offset to the previous history entry, and
return a pointer to that entry. If there is no previous entry, return
a NULL pointer.
Function: HIST_ENTRY*next_history ()
Move the current history offset forward to the next history entry, and
return the a pointer to that entry. If there is no next entry, return
a NULL pointer.