Add support for Linux Mint

Add support for Linux Mint and re-use Ubuntu install functions for derivatives.

Tested on Mint 13/14, Trisquel 6, Ubuntu 10.04/12.04/12.10/13.04, and Debian 7

==> debian-7.log <==
OK (total=15, skipped=1, passed=14, failures=0, errors=0) 
============================  Overall Tests Report  ============================

==> mint-13.log <==
OK (total=15, skipped=1, passed=14, failures=0, errors=0) 
============================  Overall Tests Report  ============================

==> mint-14.log <==
OK (total=15, skipped=1, passed=14, failures=0, errors=0) 
============================  Overall Tests Report  ============================

==> trisquel-6.log <==
OK (total=15, skipped=1, passed=14, failures=0, errors=0) 
============================  Overall Tests Report  ============================

==> ubuntu-10.04.log <==
OK (total=15, skipped=1, passed=14, failures=0, errors=0) 
============================  Overall Tests Report  ============================

==> ubuntu-12.04.log <==
OK (total=15, skipped=1, passed=14, failures=0, errors=0) 
============================  Overall Tests Report  ============================

==> ubuntu-12.10.log <==
OK (total=15, skipped=1, passed=14, failures=0, errors=0) 
============================  Overall Tests Report  ============================

==> ubuntu-13.04.log <==
OK (total=15, skipped=1, passed=14, failures=0, errors=0) 
============================  Overall Tests Report  ============================