add definition for ubuntu 13.04 (server)
break up postinstall.sh
install libdbus and fix typos on VirtualBox Guest additions
remove existing VirtualBox guest additions before installing new version
remove ruby and rubygems source after installing them
add /opt/ruby/bin to the global path
Merge pull request #677 from ngpestelos/ubuntu-13-04

add definition for ubuntu 13.04 (server amd64)