A function type rule matches a query if the query uses a function defined
in the rule. This is the desired behavior for blacklist mode operation
with `action=block`.
When in whitelist mode, all queries must match a rule to be allowed
through. For function type rules, this fact is problematic as queries that
don't use functions are blocked. The desired behavior is to allow the use
of certain functions while preventing the use of others.
The allowed set of functions should always contain the "empty set" (no
functions are used) when the filter is in whitelist mode.
674b3887c9