Fix untranslated button name defaults

Joomla form field default values are not put through JTEXT.

Rather than override (another) standard Joomla class, I am putting this
back to where it was before commit on 6 Sep 2013
aaff26710218216587a0e1d40783e9caa8d671d2.
Merge pull request #996 from Sophist-UK/fix_untranslated_form_button_values

Fix untranslated form button values