Support rake >10.0 by including Rake::DSL

When using rake versions 10.0 and above in a project, using `desc` and `task`
in the global namespace are no longer supported. As fabriation gem loads
lib/tasks/defined_fabricators.rake in the presence of rake, it generates
a warning in rake 0.9.* and errors in rake 10.*. This commit includes
Rake::DSL before loading lib/tasks/*.rake, which allows for error free
use of existing `desc` and `task`.

lib/fabrication.rb

@@ -2,6 +2,7 @@
 
 if defined?(Rake)
   require 'rake'
+  include Rake::DSL
   Dir[File.join(File.dirname(__FILE__), 'tasks', '**/*.rake')].each { |rake| load rake }
 end