Fix class names for AbstractField vs. AttributeField
Merge branch 'classname' into simple
Grid interface: iterate columns

Instead of using a "public" method which starts with an underscore
(which leads to errors if forgotten to call, and also some frameworks
prevent calling of leading-underscore methods from template code for
safety), just iterate the collection directly.

That is, instead of writing

	for row in collection.rows:
		collection._set_active(row)
		… do something with this row

you can now simply write

	for row in collection:
		… do something with this row
Merge von zuko
Merge branch 'itercoll'
TemplateEngine.render() must be overridden

so return an error. get_template() on the other hand may not have to be.
Use MarkupSafe on template output

This marks the output of FormAlchemy's render methods as safe to print
by template engines like Jinja2 which do auto-escaping of unsafe strings
Merge branch 'templating'