Mangler fixes

We experienced some issues using collective.solr with new style collections and some range criterion.

First of all: we seen a "min:max" in `ranges` dict, but Plone use "minmax". We don't know if also min:max is needed. If not: probably also tests must be updated.

New collection sometimes pass a date string not in iso format (like "12/11/2013") and `iso8601date` is not fixing it.