fields_blueprint_id_for takes root object into account

[panupan]

This fixes link_to_add when we have two nested forms on a page with different objects and they have overlapping associations. An example being Issue.attachments and Comment.attachments.

[nunosilva800]

@panupan @ryanb @lest I encountered a similar problem and I made this fix: https://github.com/Onumis/nested_form/compare/ryanb:master...master It seems more simple and it relies on the fact that the blueprint is placed inside of the form (as a first child).

If you want I can create a PR on this (note that I've only updated the jQuery javascript).