Fix the failed unit test due to a behavior change.   ConvertCell on a
String to Date is returning a String when called with a bogus date
value.  However, that apparently is being expected by the unit test.
Technically this is both wrong and an error - but don't want to do a
behavior change until we can assess any impacts up the chain
Merge pull request #1 from bkemper-pentaho/master

Fix the failed unit test due to a behavior change.   ConvertCell on aString to Date is returning a String when called with a bogus date