[patch] small change to built-in tag regroup

[Matias Hermanrud Fjeld]

This patch makes the built-in tag regroup return group objects instead of dicts.
group objects are lists, but their str()-method returns the grouper.

This changes the syntax like so:

{{ group.grouped }} -> {{ group }}
{% for object in group.list %}... -> {% for object in group %}...

Thus one can write:

{% regroup something by attribute as groups %}
<ul>
{% for group in groups %}
 <li>{{ group }}:
 {% for object in group %}
  {{ object }}
 {% endfor %}
 </li>
{% endfor %}
</ul>

The patch retains backwards compatability. One can still use the old syntax.

[Adrian Holovaty]

This doesn't add a whole lot of value, so I'm marking as wontfix.