fix oom bug in solr import
fix oom bug in solr import

solr imports where failing with an oom error from postgres complaining
about increasing a string buffer above 1GB.  it turns out that postgres
does not support a single row/field value above 1GB.  we were exceeding
that value for a small number of stories by joining all
processed_stories_id into the sentence aggregation query instead of just
the largest processed_stories_id.

berkmancenter/mediacloud,berkmancenter/mediacloud,berkmancenter/mediacloud,berkmancenter/mediacloud,berkmancenter/mediacloud