experimental/vsftpd

vsftpd improvements:
- intorduce one declarative list of options
- make docummentation strings more understandable and add missing options
  such as SSL/TLS support
- Use environment.etc."vsftpd".text because I can't think about any
  reason why a shell script should be used.
  That code was written in 2009.
Merge pull request #1060 from MarcWeber/submit/vsftpd

small vsftpd improvements