sorter: mtbl_merger_add_reader() -> mtbl_merger_add_source()
sorter: mtbl_merger_add_reader() -> mtbl_merger_add_source()

snarkmaster/mtbl,snarkmaster/mtbl,rep/mtbl,farsightsec/mtbl,snarkmaster/mtbl,rep/mtbl,farsightsec/mtbl,rep/mtbl