[form] fix validation error handling * type when possible ValidationError raised by the edit controller * don't rely on repository to check required field * turn css class used for field error message to errorMsg to avoid confusion with the error class added to input * fix css when errors are added by the form renderer * fix form renderer to add the error message

""" CW - nevow/twisted client

:organization: Logilab
:copyright: 2001-2010 LOGILAB S.A. (Paris, FRANCE), license is LGPL v2.
:contact: http://www.logilab.fr/ -- mailto:contact@logilab.fr
:license: GNU Lesser General Public License, v2.1 - http://www.gnu.org/licenses
"""