Bug#390712: Exim fix is upstream

[Phil Pennock]

As a step towards closure: the fix was committed to Exim on 2009-10-16
and was included in Exim 4.70.  Current release is 4.72, 4.73 should be
soon.

The only changes for the patch committed upstream were:
 * documentation
 * a different diagnostic for versions of GnuTLS too old to support this
   feature (the option becomes a noop, visible only with debugging).

Regards,
-Phil