Error during launch of pdfwalker

```
What steps will reproduce the problem?
1.Launch pdfwalker
2.Error during launch

What is the expected output? What do you see instead?
/home/mauburtin/.rvm/rubies/ruby-2.1.5/lib/ruby/site_ruby/2.1.0/rubygems/core_ex
t/kernel_require.rb:54:in `require': superclass mismatch for class Date
(TypeError)
from /home/mauburtin/.rvm/rubies/ruby-2.1.5/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:54:in `require'
from /home/mauburtin/.rvm/rubies/ruby-2.1.5/lib/ruby/2.1.0/date.rb:3:in `'
from /home/mauburtin/.rvm/rubies/ruby-2.1.5/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:54:in `require'
from /home/mauburtin/.rvm/rubies/ruby-2.1.5/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:54:in `require'
from /home/mauburtin/.rvm/rubies/ruby-2.1.5/lib/ruby/2.1.0/psych/deprecated.rb:1:in `'
from /home/mauburtin/.rvm/rubies/ruby-2.1.5/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:54:in `require'
from /home/mauburtin/.rvm/rubies/ruby-2.1.5/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:54:in `require'
from /home/mauburtin/.rvm/rubies/ruby-2.1.5/lib/ruby/2.1.0/psych.rb:12:in `'
from /home/mauburtin/.rvm/rubies/ruby-2.1.5/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:54:in `require'
from /home/mauburtin/.rvm/rubies/ruby-2.1.5/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:54:in `require'
from /home/mauburtin/.rvm/rubies/ruby-2.1.5/lib/ruby/2.1.0/yaml.rb:5:in `'
from /home/mauburtin/.rvm/rubies/ruby-2.1.5/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:54:in `require'
from /home/mauburtin/.rvm/rubies/ruby-2.1.5/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:54:in `require'
from /home/mauburtin/.rvm/gems/ruby-2.1.5/gems/origami-1.2.7/bin/gui/config.rb:26:in `'
from /home/mauburtin/.rvm/rubies/ruby-2.1.5/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:54:in `require'
from /home/mauburtin/.rvm/rubies/ruby-2.1.5/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:54:in `require'
from /home/mauburtin/.rvm/gems/ruby-2.1.5/gems/origami-1.2.7/bin/gui/walker.rb:50:in `'
from /home/mauburtin/.rvm/rubies/ruby-2.1.5/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:54:in `require'
from /home/mauburtin/.rvm/rubies/ruby-2.1.5/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:54:in `require'
from /home/mauburtin/.rvm/gems/ruby-2.1.5/gems/origami-1.2.7/bin/pdfwalker:4:in `'
from /home/mauburtin/.rvm/gems/ruby-2.1.5/bin/pdfwalker:23:in `load'
from /home/mauburtin/.rvm/gems/ruby-2.1.5/bin/pdfwalker:23:in `'
from /home/mauburtin/.rvm/gems/ruby-2.1.5/bin/ruby_executable_hooks:15:in `eval'
from /home/mauburtin/.rvm/gems/ruby-2.1.5/bin/ruby_executable_hooks:15:in `'

What version of the product are you using? On what operating system?
origami 1.2.7

```

Original issue reported on code.google.com by `mauburti...@nes.fr` on 28 May 2015 at 12:20