Search from a requires page doesn't work

[jamonation]

Expected behaviour:

Searching on a page with the results of a requirements query should return new search results. For example: search for a charm from https://jujucharms.com/q/?requires=pgsql - the resulting page should ignore pgsql (or better still, union the search term and pgsql to find related dependencies).

Actual behaviour:

Search does not work, instead it just returns the same set of requires results. https://jujucharms.com/q/uwsgi?requires=pgsql only shows the same 315 results as https://jujucharms.com/q/?requires=pgsql

Steps to reproduce:

1. Visit a charm page, and click on a relation: https://jujucharms.com/postgresql/187
2. Click 'db: pgsql' to be taken to https://jujucharms.com/q?requires=pgsql
3. Search on the resulting page (try any term, e.g. a charm that exists or doesn't), and the list of results will return the same pgsql dependent charms, not the charm being searched for