the size of the rendered release notes. By default, any element with
a role="historic" attribute won't get rendered in the output unless
the INCLUDE_HISTORIC Makefile variable is defined.
the release notes compare 5.0-CURRENT to 4.0-RELEASE, but in at least
one place it is beneficial to mention the last stable release of
FreeBSD (4.5-RELEASE).
Reviewed by: bmah
