Update blankslate.rb to play nicer in Ruby 1.9

Currently, blankslate causes bugs and quirks since `instance_methods` 
returns symbols on Ruby 1.9.  This patch fixes that.
Make it 1.8 compatible and slightly faster
Kill the whitespace
Merge pull request #6 from github/fix-builder-19-issue

Update blankslate.rb to play nicer in Ruby 1.9