community/perl-{app-cpanminus,math-pari}: add options="net"

perl-app-cpanminus was not working properly as it used an option only available in GNU wget. After fixing compatibility with Busybox wget, I put in a test to make sure it works and continues to be compatible with Busybox wget.

perl-math-pari requires net access to download additional sources from FTP. Aport maintainer has been notified, but as Math::PARI is not (yet) compatible with the latest version of the pari library (which we have in testing/), I don't think much can be done about this.