stylesheets (particularly with respect to translations) is now similar
to that of the doc/ tree. Added a customization for HTML page footers
(this is the only reader-visible change).
1. There is now only one RELNOTESng stylesheet; the architecture-specific
stylesheets (to handle different values of the arch= attribute) are gone.
2. Several Makefile variable definitions were factored into
doc.relnotes.mk.
Submitted by: dd