Multiple identical source files create only one database entry

[Trajan McGill]

Hash matching results in deduplication, which is good, but only one entry in a file hardlink database record group is being created for each entire backup, rather than for each individual hardlink created. This interferes with hardlink counting for purposes of not exceeding the user-specified max number of hardlinks per physical copy.

Need to consider:
-Make the hardlink max actually a count on backups using links, rather than on individual links? Main issue with this is that part of the reason for the hardlink max is things like the file system having a max number of hardlinks (e.g., 1024 in NTFS) and if we lose count, we can't stay under that. That might not be the end of the world if we fall back to full copies whenever hardlinking fails, though.
-If hashes match, but file dates don't, handle the deduplication properly.