Stopwords cause subject searches to fail

If you do a subject search for a term containing stopwords (i.e. "a farewell to arms"), you get no hits. If you exclude the stopwords, the search succeeds. This is due to the way Dismax works -- all Dismax fields should have the same form of stopword handling. In our current configuration, the "era" field is incompatible with all of the other fields. We need to clean up our handling of subject headings to solve this problem -- since the existing configuration is a bit ugly and inconsistent, this is a good excuse for improvement.