Convert timestamps to long's

not all timestamps are from this century, those from before
the year 2000 have less digits. Comparing the bytes only
is wrong in this case.
Merge branch 'master' of github.com:thelastpickle/backupify-comparator into zero-copy-TLP
Merge pull request #4 from thelastpickle/zero-copy-TLP

Convert timestamps to long's