"cannot load such file -- wiringpi/wiringpi" in ruby 2.0

[unforced]

2.0.0-p0 :001 > require 'wiringpi'
LoadError: cannot load such file -- wiringpi/wiringpi
    from /home/pi/.rvm/rubies/ruby-2.0.0-p0/lib/ruby/site_ruby/2.0.0/rubygems/core_ext/kernel_require.rb:45:in `require'
    from /home/pi/.rvm/rubies/ruby-2.0.0-p0/lib/ruby/site_ruby/2.0.0/rubygems/core_ext/kernel_require.rb:45:in `require'
    from /home/pi/.rvm/gems/ruby-2.0.0-p0/gems/wiringpi-1.1.0/lib/wiringpi.rb:1:in `<top (required)>'
    from /home/pi/.rvm/rubies/ruby-2.0.0-p0/lib/ruby/site_ruby/2.0.0/rubygems/core_ext/kernel_require.rb:110:in `require'
    from /home/pi/.rvm/rubies/ruby-2.0.0-p0/lib/ruby/site_ruby/2.0.0/rubygems/core_ext/kernel_require.rb:110:in `rescue in require'
    from /home/pi/.rvm/rubies/ruby-2.0.0-p0/lib/ruby/site_ruby/2.0.0/rubygems/core_ext/kernel_require.rb:35:in `require'
    from (irb):1
    from /home/pi/.rvm/rubies/ruby-2.0.0-p0/bin/irb:16:in `<main>'

[smiler]

The problem is due to a change in mkmf makefile generator in ruby 2.0. When the gems native extension is installed the makefile doesn't create the lib/wiringpi directory. This causes the install command to copy wiringpi.so to lib/wiringpi instead of lib/wiringpi/wiringpi.so.
An ugly workaround is to create a dummy file in lib/wiringpi and include it in the gem.