Omit the `div.form-actions` tag from inline forms.

To render an inline-form, it's current possible to pass in:

* `bootstrap_form_style=form-inline` to the form constructor
* `category=structural` / `inline=True` to your widget constructor(s)

However, it's not currently possible to pass in a kwarg to stop rendering the `div.form-actions` container around your buttons, as per the markup recommended by the bootstrap "Inline Form" docs: http://twitter.github.com/bootstrap/base-css.html#forms

This patch fixes the issue by `tal:omit-tag`ing the div.form-actions element if `field.bootstrap_form_style == 'form-inline'`.