Accession number sorting in search results is not working

[nellh]

Describe the bug If you include a full accession number in your search query, it should be heavily weighted to an exact match. At one point this was working, so this appears to be a regression.

To Reproduce Steps to reproduce the behavior:

1. Search for 'ds000005'

Expected behavior ds000005 should be the top result unless other terms are also present and override this.