work-around for problems illustrated by 2.12.0-repo dir using the snapshot as extra source + an APT preference file setting higher priority for r-* deb packages from the snapshot
r-3.0.2 working well without any workaround
removed junk files
r-3.1.1 working, with appropriate MRAN repository
Merge pull request #5 from kforner/master

first proof of concept of MRAN repos, and some work-arounds