Fix --no-check-md5

Previously, --no-check-md5 could still do file I/O to calculate the
md5sum of each file to allow for the hardlink and remote copy paths to
work.  This wasn't intended.

Now --no-check-md5 ensures that we don't do file I/O to calculate the
md5sums, thus hardlinks and remote copying of such files won't be done
either.