When incorporating a copyleft licensed program with a lax licensed program,
it is correct to preserve the original license notice.  See also:
  https://www.softwarefreedom.org/resources/2007/gpl-non-gpl-collaboration.html

base64.scm did not do this.  This is important, because it is part of
the license that the copyright header be preserved, so we must do this
to comply correctly.

(This is a common confusion: adding a stronger copyleft does not
"relicense" the original work.)

 - Chris