[PATCH] xfstests: test timestamps before the epoch

[Christoph Hellwig]

This one actually ends up failing on XFS for me:

@@ -1,5 +1,5 @@
 QA output created by 258
 Creating file with timestamp of Jan 1, 1960
 -Stat of file yields: -315593940
 +Stat of file yields: -315615540
  Remounting to flush cache
 -Stat of file yields: -315593940
 +Stat of file yields: -315615540

Note that we still get the same for both, it just seems XFS rounds it
a bit different.