Handle (or at least fudge &/ memoize) the msg_group.hash value in iOS.

[t413]

In iOS the threads table, called msg_group, has a 32-bit column called 'hash'. From what I can tell it's not the crc32, adler32, or fletcher32 checksum hash of the number field directly.

It's doubtful I'll find the exact hashing function it's using. The fallback is to memoize that value, the original number, and a 'cleaned' version of the number all together with the messages. If you're outputting to another iOS format I'll use it if it exists and fudge another hash using CRC if it doesn't.

[t413]

Actually this isn't relevant anymore. It's only part of the database in iOS 5 and earlier. I'll just be doing iOS 6+ exporting.