Add support for checking permission of page's parents.

[netcarver]

Allows you to optionally check the edit permission of each of the page's parents.

This can greatly reduce the number of pages which need to be added to a user's editable-pages list as it allows only the page acting as the container of a group of pages to be tagged as editable.

So, instead of this...

/
|- John's Tags
|         |-- Soccer (added to John's list)
|         |-- Rugby ( ditto )
|         |-- Skiing ( ditto )
|...

You only have to add the "John's Tags" page to user John's editable-pages list and all the child pages can now be edited by him.