Change how the recommended mailing list to track is
added to the footer of the release/doc/ pages by
moving a hard-coded value (that is subject to human
error to change) to release.ent where other values
are regularly changed, and adding parsing logic to
release.xsl.

Approved by:	re (implicit)
MFC after:	3 days
Sponsored by:	The FreeBSD Foundation
Add an arch.powerpc64 entity.

Sponsored by:	The FreeBSD Foundation