Run EPV on non default branch

EPV currently runs on just master, however when having a phpBB3 MOD in master, and a 3.1 extension in another branch, it is impossible to run it from the website, even when the default branch on github is the extension.

http://stackoverflow.com/questions/16500461/how-do-i-find-the-default-branch-for-a-repository-using-the-github-v3-api