[Exim] FreeBSD port updated to exim-4.21 [BE CAREFUL]

Hi folks,

The FreeBSD port for exim has been upgraded to exim-4.21.

Please note that exiscan-acl is now the default unless you define
WITHOUT_EXISCAN for the build.

The non-ACL exiscan patch is no longer supported.

This means that existing installations that previously relied on the
non-ACL exiscan patch CAN NOT be upgraded without changes to the Exim
configure file.

That said, such changes shouldn't take you too long. Took me less than
5 minutes on my testbed.

Apologies for any inconvenience caused. Not big apologies, though,
since it's high time people stopped using the non-ACL exiscan patch. :-)

Ciao,
Sheldon.