install: run bundler --local install only if cache directory is present.
dockerfile: combine vim installation with previous apt-get install command
dockerfile: run ruby compilation after installing packages using apt-get.

basically to improve cache hits while updating the ruby package.
dockerfile: update ruby package to patch level 353
install: upgrade to gitlab-6.3.1
install: upgrade to gitlab-shell-1.8.0
README: cleanup
dockerfile: install python2.7 explicitly