SnapRAID v9.3

• Fixes an invalid assumption in the copy detection mechanism that
  could result in an internal inconsistency, and with the impossibility
  to run the 'sync' and 'diff' commands.
  This was triggered by a very specific pattern of identical files.
  At least three of them, with one already in the parity, and at a
  higher disk number than the others that should be instead new ones.
  This had no bad effect, if not preventing the 'sync' command to run.
  A workaround was to just run 'sync' one time with the -N, --force-nocopy
  option to disable the copy detection.
• Restored the -O2 optimization option for Windows binaries, as -Og has a
  too big performance penality.