Stubbing out 'disown-opener'.

w3c/webappsec#517 asked for this, and it's a totally reasonable thing to do.
But, w3c/webappsec#139 asked for the inverse ('disown-openee' or something),
and it's not clear to me whether there's a good syntax that might encompass
both.

Leaving both tickets open until we come up with something we're happy with.
Until then, puttign this stub in place.

Author: mikewest