DateTime field has to keep the value entered by the user when the validation failed.
Currently, the test will fail, as it is not the current behaviour of the Field. This bug has to be fixed.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@13876 20353a03-c40f-0410-a6d1-a30d3c3de9de