Homebrew/homebrew — pull request #29218 by mikemcquaid (2014-05-13 10:31:15+00:00)
Title: download_strategy: fix Git repo updating.

Git repositories should always be updated when the ref is a branch. They should be also updated if no ref was specified or if the ref isn’t present. This stops the repo being updated if we’re building a specific revision and it is present. Additionally, this stops the update barfing on repositories where we’re using a revision and there is no upstream `master` branch.