Index delegateable frozen state in Solr (needs reindex)
Allow to specify OR-filters in SolrPager

This allows to specify an additional filters with multiple alternatives
(logical OR).

The extra_filter and alternatives_filter parameters only allow for
certain and not arbitrary logical combinations: those which are
currently required in Adhocracy.
Use SolrPager for milestone proposal pager
add comment on reduce expression
Merge pull request #865 from nidico/feature-milestone-solr-pager

Solr-based milestone proposal pager