gregbell/active_admin — pull request #1647 by dapi (2012-09-06 18:19:08+00:00)
Title: Support automatic use of decorators

## Background
See discussion at #1079.

All of this is consistant with the jcasimir/draper api, but does not specifically require draper.
It is also fully backwards compatible for folks that do not use decorators.
Fixes problem with tests of original request https://github.com/gregbell/active_admin/pull/1117

## Notes
Because of the pagination and scoping in ActiveAdmin, this requires that #decorate return a
collection proxy and not just an array of decorators. This is the case in jcasimir/draper starting at v0.9.3.