deploy:setup fails when the repo uses the specified (non-master) branch as its base.

[marc]

When deploy:setup checks out a repo and a non-master branch is specified, the checkout command fails if the repo uses that branch as its base. (Ex: git clone of a repo that uses mybranch as the base (default) instead of master would already be on the mybranch branch from git clone. Then git checkout -b mybranch … would fail with "fatal: A branch named 'mybranch' already exists.")

[marc]

Issue #4 is the pull request with a fix.