added feature to create orphan branches

This pull request also contains two fixes: one for test execution under Ruby 2.1.1 and one for the usage of '-b' used in lib.checkout. Just merge the orphan support commits, if you do not want to merge these fixes. I added/extended the test cases for all the changes I have made.

By the way: when will be the next release date, so that I can switch back from my custom gem to the rubyforge-release as soon as the feature to create orphan branches is merged?