Don't include atime when determining hardlink compatibility.

Don't include the atimes since we're comparing two paths stat()ed at
different times, and depending on the
platform/filesystem/mount-options, that may result in two different
atimes, even when the paths refer to the same file.

Thanks to Alexander Barton <alex@barton.de> for tracking down the
problem.

Signed-off-by: Rob Browning <rlb@defaultvalue.org>
Reviewed-by: Gabriel Filion <gabster@lelutin.ca>