Improve network performance for VirtualBox

Without those lines, VitrualBox machines are being very slow with all network operations (tested only in OS X Lion, but they are supposed to work everywhere). See https://github.com/mitchellh/vagrant/issues/1807
Split stdout stderr for non-tty commands
Add stderr unit test
Make StdCopy works with huge amount of data
Add documentation
abord build if mergeConfig returns an error and fix duplicate error message
Fix attach issue
Improve detach unit tests
Fix minor typo

Changed  to
Merge pull request #1952 from metalivedev/1909-cherrypick

Fix minor typo
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
Add proper bash completion for "docker push"
Merge pull request #1948 from dotcloud/fix_attach

Fix attach issue
Update tar dependency to newest version
Merge pull request #1967 from dotcloud/vendor-update-tar

Update tar dependency to newest version
Hack: remove deprecated files
hack/MAINTAINERS.md: a maintainer's manual.