Superseded: Avoid Overwriting existing repos when installing a new repo

Superseded by: Merge Request #21 Add keep epoch env var no global rtn&fix issue 74 (avoid overwrites in ~/sources*)

This fixes the issue Issue #74 ppa2pup overwrites main repos if either the tor or node.js repositories are in sources.list but only when ppa2pup_gawk is used to update the repos defined in /etc/apt/sources.list

There is a related issue ppa2pup: allow distro other than "$DISTRO_BINARY_COMPAT" that will be dealt with in a seperate merge request.