Remove trailing slash from import volume.
Add rsession.conf with a default repo.
Add apt-get update after changing sources.list.
Add locale.
Use the squeeze-cran3 repo for R 3.x.
Update rstudio-server.
Add package update step.
Merge pull request #2 from fhcrcio/rebase-upstream-redux

Fix a few Dockerfile issues and update R to 3.x