Add -g option to generate animated gif archive
Replace 'sh' from Rake::FileUtilsExt to 'system'
So that we could run single aruba test
Add aruba tests for gif generation
Fix keep_if for ruby 187
Fix Time#to_date issue for Ruby 187

Somehow Time#to_date is a private method in Ruby 1.8.7...
Merge pull request #95 from hSATAC/feature/animated_gif_archive

Add -g option to generate animated gif archive