Improve generated bin/setup

* Make script idempotent.
* Fail fast with install messages and non-zero exit status.
Ha, whoops.

On Tue, Sep 30, 2014 at 4:21 PM, Derek Prior <notifications@github.com>
wrote:

> In templates/bin_setup.erb:
>
> > @@ -7,6 +7,10 @@
> >  set -e
> >
> >  # Set up Ruby dependencies via Bundler
> > +if ! command -v bundle > /dev/null; then
> > +  gem install bundler --no-document --pre
>
> I don't think we should be scripting a pre-release install of bundler.
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/thoughtbot/suspenders/pull/412/files#r18253900>.
>