Revision 1915101

Follow-up to r1905955, fix randomly failing store_pristine_tests.py 9, 10, 11
and 12 due to `apr_stat` which gives only a resolution of seconds on macOS.

* subversion/tests/cmdline/store_pristine_tests.py
  (simple_diff_with_pristine): Sleep for timestamps change.
  (simple_diff_without_pristine): Ditto.
  (simple_revert_with_pristine): Ditto.
  (simple_revert_without_pristine): Ditto.