`bundle config --local gemfile /foo/bar/MyGemfile` now works
- `bundle config` can be used to set a custom gemfile name for a
  project (specifying an absolute path)
- using other bundle commands will now search up parent directories
  for a .bundle dir and use the gemfile specified in .bundle/config if
  it is set
- does not require a file named 'Gemfile' to exist
- Revert "Correct bundle-config manpage"
  This reverts commit 0a814573363d48f8cd860d672f1c935fe1d89fca.
- An added bonus: you can now both set and *delete* a global bundler
  setting from *anywhere*: `bundle config --delete foo`