(refs #2882) add sfValidatorDateTest +38 case

about test case
  empty values:     ('', false, array(), new SimpleXmlElement('<hoge />'))
  not empty values: (0, '0', 0.0)

  required:         (true, false)
  date array:       (Yms, YmsH)
(refs #2882) fixed not to evaluate empty array in preg_match
(refs #2882) fixed not to be empty for zero number or string
(refs #2882) fixed not to be empty day values for zero number or string
Merge branch 't2882' (fixes #2882)