update to support inherited resources 1.3.0

[fabiormoura]

Please, forgive me if I made some mistake because I never used github and git. I followed the tutorial of https://github.com/gregbell/active_admin/blob/master/CONTRIBUTING.md to help me to contribute to active admin project . I ran all tests and all tests passed.

[amalagaura]

I believe there are other issues holding it back : #808

[fabiormoura]

I can not understand your argument. I had read the issue 808 before I've created this fork. What motivated me to create this fork was the fact that inherited resources 1.3.0 provides support to mass assignment roles which is a new feature of Rails 3.1. I modified active admin to support this changing and I ran all tests before make a pull request. I did anything wrong?

[amalagaura]

Greg mentions there are reloading issues which are breaking ActiveAdmin. Maybe that is old information. It is possible that the app has problems in development mode which the tests are not picking up. I am not sure, I do not know the details unfortunately.

[fabiormoura]

I don't know if my fork presents some problem in development mode but I'm using it as replacement for the active admin gem in a project. I'm using this fork for a week and I did not find any problem yet.

[mitio]

I can confirm that all tests are passing with this change on Ruby 1.9.3-p0.

+1 for this PR. I think the new mass assignment feature in Inherited Resources 1.3 is a must for almost any project. I have no idea how things worked before :)

[gregbell]

Merged in to master. Thanks @fabiormoura!