add is_advanced_search? check to #add_advanced_parse_q_to_solr

[codeforkjeff]

#add_advanced_parse_q_to_solr wasn't making the check to see if the search is an advanced search. This was interfering with an extension we're working on in this repository: https://github.com/upenn-libraries/blacklight_solrplugins

#add_advanced_search_to_solr is already making this same check, so this brings the two processor methods in line with one another.

[cbeer]

I think this will break the Boolean query parsing for the single search box query (although it seems like we're missing an integration test for it..).

[codeforkjeff]

Yes, you're totally right, sorry about that. I'll have to think about another way to deal with the conflict with blacklight_solrplugins. Closing this PR.