Enable source-only for an apt repo entry. 

Currently the module can enable a repository and its associated source repository, but cannot enable the source repository by itself. Why is this desirable? Well, in our case at least, we maintain a full binary mirror but do not maintain a source mirror. We want to include our mirror "deb http://company.example.com squeeze main non-free contrib" but we want source packages to come from official Debian mirrors; "deb-src http://ftp.us.debian.org/debian squeeze main non-free contrib". The puppetlabs::apt module will not allow that as-is; this simple modification to the .pp and to the source.list.erb template allows it. Set "include_src" and "src_only" to true, and the entry in the sources.list.d/${name}.list will contain only the "deb-src" line, without the "deb" line.