Allowing ``register_filter`` to override pre-registered filters.
Allowing ``register_filter`` to override pre-registered filters.

This lets us customize filters for various environments by overriding the
built-in (pre-registered) filters.

heynemann/webassets,scorphus/webassets,wijerasa/webassets,0x1997/webassets,JDeuce/webassets,JDeuce/webassets,florianjacob/webassets,john2x/webassets,heynemann/webassets,aconrad/webassets,florianjacob/webassets,aconrad/webassets,heynemann/webassets,0x1997/webassets,glorpen/webassets,glorpen/webassets,wijerasa/webassets,aconrad/webassets,glorpen/webassets,scorphus/webassets,john2x/webassets