Fix ugly error messages in just-init'ed repo

[nvie]

$ git flow init
...
$ git flow start feature xxx
fatal: 'origin': unable to chdir or not a git archive
fatal: The remote end hung up unexpectedly
Remote branch 'origin/develop' does not exist and is required.

[hollow]

the question is if git-flow should work without a remote. if so, the branch equal checks have to be refactored too.

[nvie]

Fixed with the new implementation of git flow init.