Make gem "ruby-debug19" require ruby-debug

Gemfile

@@ -31,7 +31,7 @@ end
 
 platforms :mri_19 do
   # TODO: Remove the conditional when ruby-debug19 supports Ruby >= 1.9.3
-  gem "ruby-debug19" if RUBY_VERSION < "1.9.3"
+  gem "ruby-debug19", :require => 'ruby-debug' if RUBY_VERSION < "1.9.3"
 end
 
 platforms :ruby do