Enabling the translation of petitions

Issue Summary

With the content translation module (inlcuded in Drupal core), it is possible to translate contents.

1/ Enable the translation module
2/ Go to admin/content/node-type/petition
3/ Under the Workflow fieldset, Multilingual support, choose "enabled with translations"
4/ Enable extra languages for your drupal sites under admin/settings/language.

Normally, when you then choose "translate" on a node menu, it copies the whole node type as a new node, with reference to the node with the original version.

In the case of petition module, I thought it would be a problem, because the signatures would only appear under the translated version the petitioner signed on.

I may want to create a petition in 10 languages, but all the signatures should appear under each translated version and only I, the author of the original version should be able to administer the signatures and petition settings.

I have done some changes in the code to make it possible.
I have done some sucessful tests so far, but it may interact with other drupal applications which I may have neglected.
So please test the dev version.