new syntax for RequiredValidUntil filter

[Rod Widdowson]

> Why not REQUIRE @maxValidity instead?

We cannot, that would break backwards compatibility.  It might be compatibility against broken behaviour but we still cannot break
configurations (I maintain). At least in 3.4 you'll get a warning for that sort of non-sense.

> but it makes no sense.
None at all, I agree.  It's been a thorn in my side since V2 days

> There's probably a good reason.

Again , backwards compatibility, as is the fact that maxValiditydInterval can be a value in seconds or a Duration (rather than a
value in milliseconds or a Duration like every over Shibboleth controlled setting).  That is why we introduced maxValidity (which is
milliseconds or Duration)

In short, it's a mess.  In V4 you should expect to see the default value become 14 days (or some such value).  This is all part of
clearing the decks to allow us to make a compatible change in V4 for sensibly configured systems, there are others in the pipe (see
for example the Dependency stuff - expect <Dependency> to go away in V4.

/Rod