in text: Base64 -> Base 64

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/exams@618 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
small modifications in code/documentation of base64 option to suppress supplements

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/exams@619 edb9625f-4e0d-4859-8d74-9fd3b1da38cb