This allows users to tell Bundler where to put the binstubs for system gems, much like the -n option in ~/.gemrc for Rubygems. If you set one, it probably makes sense to set the other. If you don't set system_bindir, though, Bundler will install system binstubs into Gem.bindir, regardless of what Rubygems does. refs #1417
Conflicts: .travis.yml lib/bundler.rb lib/bundler/source.rb
(re-enabling Bundler 1.0.x compatibility on Rubygems 1.8.10)
…imes with a different set of groups.
The mkdir_p was originally added for JRuby (see #602). As of JRuby 1.6, some paths will actually raise an error, so we need to rescue and ignore those.