Remove 'exists' check when doing a View permission check, otherwise it always returns false and gridfield never works
3.1 updates to DataService to handle mutated lists returned by DataList
FIX Minor 3.1 updates

* Fixed redirect after adding new Access Authority
* Made sure list displaying applied access is filtered correctly
API Introducted RestrictedList

Added DataList child class RestrictedList to provide more consistent API,
still need to fix the population of listing if the listing doesn't have
all the objects filled to LIMIT

Removed obsolete PermissionTableField class
Change restrictedList required perm method name
FIX Ensure limit() return value is re-assigned to manipulated list object
FIX Work around gridfield triggering access to a null object submitted in #7
API Added impl for RestrictedList::byID()
API Added RestrictedDataList extension

- Added RestrictedDataList to all for calling things in the format of

```
DataObject::get()->filter('Title', 'Thing')->restrict();
```

  for applying permissions

- Cleanup some of the DataService functionality that touched on similar
  functionality

- Exposed PermissionParent objects via CMS ui for permission management in
  those projects that use it
API Added ContextUser global template var

Added $ContextUser as a global template variable as an alternative to the
$CurrentMember var which will hit the DB _every_ single time and create a new
object instead of returning the originally logged in user
FIX Output pjax header to prevent incorrect redirects/page loads on CMS requests
API Do local caching of data in PermissionService

- PermissionService now contains a local cache of data object parents and
  group assignments to avoid costly recursive hierarchy queries where they
  occur
FIX Fixed missing method reference in Restrictable
Increased default cache timeout for restricted object permissions
FIX restricted list re-queries to full limit

* Fixed the restricted() method on the list decorator to ensure the returned
  list containtains as many elements as needed to match the supplied limit.
* Fixed test cases for needed items
FIX Updated cache lifetime for permissions to be 1hr by default
Merge branch 'master' of git://github.com/nyeholt/silverstripe-restrictedobjects
FIX Further fixes to how the QueryOffset is calculated and added into the restricted list