[PS1] Entries for game revisions are lost during database compilation

[pmartycz]

Currently source dat files are merged using rom.serial field which is not unique across game revisions. This results with entries for earlier revisions being clobbered by newest one.

Here's a demonstration of this behavior taking venerable Tomb Raider as example

$ c_converter out.rdb metadat/redump/Sony\ -\ PlayStation.dat
$ c_converter out-rom-serial.rdb rom.serial metadat/redump/Sony\ -\ PlayStation.dat
$ printf SLUS-00152 | hexdump -v -e '/1 "%X"'; echo
534C55532D3030313532
$ libretrodb_tool out.rdb get-names '{"serial": b"534C55532D3030313532"}'
"Tomb Raider (USA) (Rev 5)"
"Tomb Raider (USA) (Rev 4)"
"Tomb Raider (USA) (Rev 3)"
"Tomb Raider (USA) (Rev 2)"
"Tomb Raider (USA) (Rev 1)"
"Tomb Raider (USA)"
$ libretrodb_tool out-rom-serial.rdb get-names '{"serial": b"534C55532D3030313532"}'
"Tomb Raider (USA) (Rev 5)"

Perhaps rom.crc should be used instead as is the case for other systems?