The perl command line which is responsible for replacing
ftp.debian.org with the according snapshot.debian.org entry
produced an invalid sources.list entry with perl v5.14.2,
e.g. generating:
| deb http://snapshot.debian.org/archive/debian/
20150622/ main deb-src http://snapshot.debian.org/archive/debian/
20150622/ main
with the following input:
| deb http://ftp.debian.org/debian/ jessie-backports main
| deb-src http://ftp.debian.org/debian/ jessie-backports main