replace dataflow with simpler Thread code, remove dataflow dependency
Remove Future models
Extract a Propagate model that installs the gem for us
Revert "Always checkout detached branches, we never want tracking branches in cached-copy."

--detach is not available on the installed version of git

This reverts commit 204e4e38c9b7f5ee078f2493c5d9dcf5e4f5afb1.

Conflicts:

	ChangeLog.md
Clean up local branches that might interfere with the checkout.

This hopefully prevents the problem where an old branch does
not get properly updated when checking out.