[Exim] OpenBSD exim port updated to 4.xx

If anyone want to know, I have this morning updated the exim port in OpenBSD
to 4.41 (from 3.36) after some badgering and offers of code...

It includes exiscan by default, but this can be left out using the
no_exiscan flavor.

Please feel free to report OpenBSD port specific issues direct to me or my
co-maintainer, listed in the port Makefile.

Peter