Implement access hook.
Make display respond to access callbacks.
Squash dsm() and fix access on policy management.
Prevent the purge form from showing at all times.
Fix ingest permissions...

...  Was allowing on any object... Should only be collections.
Fix use of constant.
Fix too permissive handling of FEDORA_INGEST.
Add testing of hooked access hook implementation.
Fix/flesh out function comment.
Fix a couple issues with the tests.

Introduction of the hooked access callback made FEDORA_METADATA_EDIT
required for change the COLLECTION_POLICY and RELS-EXT for the
respective collection management functions.

Dependent on https://github.com/Islandora/islandora/pull/358.
Merge pull request #67 from adam-vessey/7.x-hooked-access

7.x hooked access