According to David it makes no sense to use scoring functions designed for human languages in the context of queries for strings like "P180=Q42", and we ought to use ConstantScore queries instead

Acceptance criteria:

• if you look at http://<wiki>/w/index.php?search=SEARCH_TERM&ns6=1&mediasearch=1&cirrusDumpQuery you should see that queries for "PXXX=QYYY" are constant_score rather than match queries in the should section of query
• if you look at http://<wiki>/w/index.php?search=SEARCH_TERM&ns6=1&mediasearch=1&cirrusDumpResult&cirrusExplain=pretty you should see that there's a "Constant scored query" section for each result where we have a match for "PXXX=QYYY"