Adapter for groupby_modifier should be orderable #222
Description
Scenario:
install collective.collectionfilter and collective.taxonomy and a custom addon. register your own adapter for groupby_modifier
if you forget explicit to load collective.taxonomy before your adapter registration happen, then the adapter of collective.taxonomy wins. and your own adapter does'nt work properly
we need a orderable adapter implementation like in plone.outputfilter or ...?