adjust Debian source.list file to enforce installation of apt-get packages

[krichter722]

Currently the usage of setup/prerequisite scripts is unclear (#7). As soon as it is, Debian source.list file should be adjusted to install perl scripts when apt-get build-dep vboxadm is invoked.

This might become invalid after #7 is fixed and installation takes place in contrib/inst_deps.pl. Currently it is necessary to invoke apt-get install perltidy libnamespace-autoclean-perl libcrypt-cbc-perl libdate-pcalc-perl libemail-date-format-perl libtext-levenshtein-perl libmail-pop3client-perl libcourriel-perl libcgi-fast-perl after perl contrib/inst_deps.pl && apt-get build-dep vboxadm which shouldn't be the case.