Fix ArrayIndexOutOfBoundsException in CreateBranchCommand
If remote name contains / or there was a branch directly under the
refs/remotes namespace (wrong) the computation of remote name and
suggested local branch name would fail. Fix this by looking at the
configured remotes. A ref under refs/remotes that does not match a
remote configuration is not considered a remote tracking branch anymore.
This patch does not fix all similar errors in EGit/JGit.