added guardian as optional requirement, stubbed out object-level permission class
some properly failing tests, set up for standard permissions
Support customizable view EXCEPTION_HANDLER

Add `api_settings.EXCEPTION_HANDLER` to support custom error responses.

Fixes #907.
Add EXCEPTION_HANDLER docs to exception docs
Merge pull request #1092 from rouge8/custom-exception-handler-setting

Support customizable view EXCEPTION_HANDLER (#907)
Extra docs on custom exception handling.
necessary test settings for guardian
first pass at object level permissions and tests
switch to a dedicated filter for read list object permissions
removed unnecessary guardian req and view.action parsing
better doc for object permissions, drop redundant has_permission call
Update release-notes.md
Add order_by to the AutoFilterSet

`AutoFilterSet` should contains `order_by` set to all by default.
Merge branch 'master' of git://github.com/bwreilly/django-rest-framework into bwreilly-master
Tweaks and docs to object-level model permissions.
Updated release notes
Add Django Guardian to travis testing
Added @bwreilly for awesome work on #1093.  Thanks!!!
Version 2.3.8
small typo correction on ViewSet example code