MPQ sector checksums are not implemented

[Nihlus]

Checksums in MPQ archives are... wonky, and are not implemented yet. This causes some files to come out with checksums on the end, and some files report themselves as having checksums despite not actually having them. Possibly an issue with the flag enum.

[Nihlus]

Notes taken from MPQ.cs, pasting here for reference:

// TODO: If Checksums are present (check the flags), treat the last sector as a checksum sector
// TODO: Check "backup.MPQ/realmlist.wtf" for a weird file with checksums that is not working correctly.
// It has a single sector with a single checksum after it, and none of the hashing functions seem to
// produce a valid hash. CRC32, Adler32, CRC32B, nothing.
// Some flags (listfiles mostly) are flagged as having checksums but don't have a checksum sector.
// Perhaps related to attributes file?