Add .dockerignore so we don't include the whole git repo in the image
Combine build steps into one RUN that leaves no waste behind
Prefer bundled libraries over system versions, as upstream does
Switch to Debian Wheezy for a more stable base
Merge pull request #2 from mwcampbell/docker-r2.6.1

Shrink the image; use bundled libraries; use Debian Wheezy