temporary helper to get a member by display name
river.parsed_query: find member by display name

This is only a temporary feature to avoid regressions.  This should be
removed once all river queries have been updated.
tests: remove misleading test

If a :spring query is given for something that is not a spring, the
query will be ignored.  It won't actually prevent a pool post from
appearing in the river.
tests: river.parsed_query should ignore invalid spring queries
tests: simplify
tests: add test with multiple regular terms for clarity
include global queries in parsed_query

This will likely change later.  If a client of parsed_query wants to get
global queries as well, it should probably indicate this.
express river.matches_post? in terms of parsed_query
optional list of keys matches_post? should ignore
refresh_posts: use parsed_query instead of query_parts