[exim-dev] branch exim-4_91+fixes created

For distro maintainers, and similar, as per Subject
and similar to previous +fixes branches.

Intent is to only carry actual fixes, no new features or
minor fiddling. The master branch remains the main path
of development; this one is subsidiary but may be of
interest to distro maintainers wanting to keep abreast
of fixes as they arrive but not at the bleeding-edge.
--
Cheers,
Jeremy