Make pattern assigned to group editable with the node tool

[su_v]

Follow-up report to
Bug #674109 “Pattern spam when adjusting a pattern in text.”
<https://bugs.launchpad.net/inkscape/+bug/674109>

Quoting comment #9:
«(…) you can not directly edit a pattern assigned to a group. You can only edit the pattern for each object in the group one at a time.»

It works with the shape tools, but not (as expected) with the node tool - seems the same issue as it was previously with text objects, see
<http://article.gmane.org/gmane.comp.graphics.inkscape.devel/35286> and
<http://bazaar.launchpad.net/~inkscape.dev/inkscape/trunk/revision/9868>