So far, enforcing authentication for query operators which require it
was done by matching an error message. Problem with this approach is,
if the query operator is invalid (as, for example, "has:starss") this
invalidates the web session for the logged in user.
Create a new exception QueryRequiresAuthException to explicitly handle
the case where an operator requires authentication and throw this when
needed instead of the generic QueryParseException.
Bug: issue 6657
Change-Id: I93096ec3b0918f8238cf2eeef96cf2cf42410e72
27e3f374ee