Better exception handling

CocoaPods-like exception handling.
A task from https://trello.com/c/6lQMHxS6/60-improve-exception-handling

oh heyyy, that’s a really good point. I’ll change it.

> On Nov 30, 2014, at 9:50 PM, Kir Shatrov <notifications@github.com> wrote:
> 
> In lib/bundler/env.rb:
> 
> > @@ -33,11 +37,13 @@ def report
> >          end
> >        end
> >  
> > -      out << "\n\n" << "Gemfile\n"
> > -      out << read_file("Gemfile") << "\n"
> > +      if print_gemfile
> > +        out << "\n\n" << "Gemfile\n"
> > +        out << read_file("Gemfile") << "\n"
> @indirect <https://github.com/indirect> should we change it to ENV['BUNDLER_GEMFILE']?
> 
> —
> Reply to this email directly or view it on GitHub <https://github.com/bundler/bundler/pull/3271/files#r21071411>.
>