ignore Bundler binstub-generated directories

I run my `bundle install` commands with the `--binstubs` option so no 
`bundle exec` is required.  This commit ensures the generated 
directories are properly git ignored in generated cookbooks.
Merge pull request #309 from schisamo/gitignore-bundler-binstubs

Ignore Bundler binstub-generated directories
If a relative :path is in Berksfile, keep it relative in Berksfile.lock.

It's inconvenient to have absolute paths in Berksfile.lock 
when it is under version control and shared.
Merge pull request #310 from rectalogic/relative-path

If a relative :path is in Berksfile, keep it relative in Berksfile.lock.
style refactors from previous commit