X-GNATS-Notify replacement

[Adrian Ashley]

In February, support for X-GNATS-Notify was removed from Gnatsweb - for
understandable reasons, given that gnatsd doesn't support it - but can
anyone remember the plan for its replacement?  I recall (but can't find) a
proposal for a new standard field in gnats-4.0.  Has anyone done this
already?  I'm trying to migrate an installation from 3.113 to 4.0 and this
is causing some head-scratching.

Thanks,
A Ashley