Only check content of files if both files have zero nanosecond times.
A zero nanosecond time is considered ambiguous as to whether or
not the timestamp has been truncated by tar. Previously the diff
algorithm was attempting to account for comparisons from a source
to a directory with an applied tar. This condition is no longer
relevant since there is no support for recreating tars directories
which have had a tar extracted. In the case where the older directory
has a truncated timestamp and the newer one does not, this may always
be considered a change. In the case where both are zero, treat the
timestamp as ambiguous and compare content.
Signed-off-by: Derek McGowan <derek@mcgstyle.net>
88d59d37fa