The shell now takes a message's signed attributes where it took a digest,
so a page can't get a login or TLS digest signed. A quiet option lets a
plugin answer from what's allowed, for anything the user didn't ask for.
An admin's install no longer covers the certificates on someone's own
computer: a managed plugin gets `keystore` when that person says yes, also
when an update adds it, and it's forgotten once everyone has signed out.
Changed test assertions: the fixture plugin needs a grant now, as managed
alone is no longer enough, and the bridge gets an options argument.
Linus Rath