Merge pull request #1901 from jalateras/update-contributring-docs

Fix #1664
Merge pull request #1932 from jcassee/patch-1

Download Ubuntu 13.04 repository key over HTTPS
Merge pull request #1929 from tianon/gentoo-docs

Simplified Gentoo install instructions now that our overlay is in the official layman repositories.xml list
Merge pull request #1954 from metalivedev/1901-cherrypick-builddocker

1901 1929 1932 cherrypick to release and docs