'git branch' when origin branch with same name exists

hi,

After helping someone on IRC who got themselves into a bit of a problem, I have a feature request for git.

In this case, the user wanted to checkout a branch of a module.  They did:

  git clone git://git.gnome.org/gtk+
  cd gtk+
  git branch gtk-3-4

Obviously this is a user error, but it's a pretty innocent one, and puts the user in a bad state.  When they figure they should have typed "git checkout gtk-3-4" it is already too late -- they will be taken onto their locally-created copy of the master branch.

So feature request: 'git branch' should not allow creating a local branch that has the same name as a branch that already exists on 'origin' (or any remote?) without some sort of --force flag.  It could instead helpfully say:

  """

    The branch you are trying to create already exists on the origin.
    Are you sure you don't want to checkout this branch using
    'git checkout gtk-3-4'

 """

or something like that.

Thoughts?