HEADS UP: sendmail 8.15.2 imported, change in IPv6 behavior

As documented in the release notes and UPDATING, the following changes accompanies the merge of sendmail 8.15.2 to HEAD:

	sendmail has been updated to 8.15.2.  Starting with FreeBSD 11.0
	and sendmail 8.15, sendmail uses uncompressed IPv6 addresses by
	default, i.e., they will not contain "::".  For example, instead
	of ::1, it will be 0:0:0:0:0:0:0:1.  This permits a zero subnet
	to have a more specific match, such as different map entries for
	IPv6:0:0 vs IPv6:0.  This change requires that configuration
	data (including maps, files, classes, custom ruleset, etc.) must
	use the same format, so make certain such configuration data is
	upgrading.  As a very simple check search for patterns like
	'IPv6:[0-9a-fA-F:]*::' and 'IPv6::'.  To return to the old
	behavior, set the m4 option confUSE_COMPRESSED_IPV6_ADDRESSES or
	the cf option UseCompressedIPv6Addresses.

Note that when sendmail 8.15.2 is MFC'ed to stable/{10,9,8}, for the sake of POLA, the default will be to continue using compressed IPv6 addresses as it has always done.  This default change will only affect FreeBSD 11 and later (and can be changed in your configuration file as described above).