Allow case insensitive searches on words not in index.

Case-insensitive search doesn't work when the query doesn't exist in the typed case. e.g. on http://bookworm.culturomics.org/arxiv/, searching for GRAPHene won't match any of the matches for 'graphene' or 'Graphene' or any other iteration. Any string that has at least one result in case-sensitive search will work as expected as a case-insensitive query.
