Allow roles to be installed from archives on github

Ensure that the automated scm determination for github.com
repos still copes with .tar.gz archive files.

Handling .zip archives is left as an exercise for the interested reader
Merge branch 'galaxy_github_archive' of git://github.com/willthames/ansible into devel

Conflicts:
	lib/ansible/utils/__init__.py
Update tests for ansible-galaxy CLI additions.