Make directory action work with Ruby 2.0

Since
https://github.com/ruby/ruby/commit/f65e683ccc3b6689ac00e7c1fe0fd2c0384824b2
dot files are only listed when using FNM_DOTMATCH.
Do not install debugger for Ruby 2.0
Merge pull request #289 from rafaelfranca/ruby-2

Make directory action work with Ruby 2.0