+/** \brief reads one item key from an 'and' set
+ \param rfd set handle
+ \param buf resulting item buffer
+ \param term resulting term
+ \retval 0 EOF
+ \retval 1 item could be read
+
+ Has to return all hits where each item points to the
+ same sysno (scope), in order. Keep an extra key (hitkey)
+ as long as all records do not point to hitkey, forward
+ them, and update hitkey to be the highest seen so far.
+ (if any item eof's, mark eof, and return 0 thereafter)
+ Once a hit has been found, scan all items for the smallest
+ value. Mark all as being in the tail. Read next from that
+ item, and if not in the same record, clear its tail bit
+*/