This adds support for `redirect=` filters. As with `removeparam=`
filters, `redirect=` filters can only be enforced when the
default filtering mode is set to Optimal or Complete, since these
filters require broad host permissions to be enforced by the DNR
engine.
`redirect-rule=` filters are not supported since there is no
corresponding DNR syntax.
Additionally, fixed the dropping of whole network filters even though
those filters are still useful despite not being completely
enforceable -- for example a filter with a single (unsupported) domain
using entity syntax in its `domain=` option should not be wholly
dropped when there are other valid domains in the list.
Raymond Hill