[exim] Need warning to exim-announce about DK drop

Since Exim 4.70 will not include support for Yahoo Domainkeys, any
existing installation with a "o=-" DK record will need to remove it before
they may upgrade from 4.69.

If the DNS and mailserver itself are maintained by separate entities,
then this DNS change may take more time than recompiling the server.

So, it would be of benefit if a warning message were posted to
exim-announce *now*, so that any such Exim installations can begin
undeploying DK immediately. Then, they can deploy Exim 4.70 at full speed
once it is released.

---- Michael Deutschmann <michael@???>