By having Filter.canonicalize_tuple() call filter_term(),
we make it so that Filter objects get operator/operand
fields in their terms when we initialize this.
This mostly caused test breakage for tests that were doing
assert.deepEqual; now we just check to make sure that the
field we need are there.
(imported from commit 63b2516dc72edeb11e76a1fa4442570b9c605baa)