Update nanosecond diff comparison

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>

fs/path.go

@@ -71,9 +71,9 @@ func sameFile(f1, f2 *currentPath) (bool, error) {
 			return false, nil
 		}
 
-		// If the timestamp may have been truncated in one of the
+		// If the timestamp may have been truncated in both of the
 		// files, check content of file to determine difference
-		if t1.Nanosecond() == 0 || t2.Nanosecond() == 0 {
+		if t1.Nanosecond() == 0 && t2.Nanosecond() == 0 {
 			var eq bool
 			if (f1.f.Mode() & os.ModeSymlink) == os.ModeSymlink {
 				eq, err = compareSymlinkTarget(f1.fullPath, f2.fullPath)