minor config feature for action_view: html_options for div tag that wraps authenticity_token

The DIV tag generated inside form_for and form_tag by default has the
style 'margin:0;padding:0' and the input fields inside it (_method and
authenticity_token) are hidden, so it usually has no effect on the
HTML page, but sometimes you need to have a CSS class on it to avoid
some layout/float issues.

This patch adds a configuration option that can be used like this:

config.action_view.html_options_for_extra_tag_in_form =


config.action_view.html_options_for_extra_tag_in_form =
{:class=>'hideMe', :style=>'display:none'}