use djangos default permission_denied view instead of the raw HTTPResponseForbidden

In the section "Using page request processors" use djangos default permision_denied view instead of the HttpResponseForbidden. This will automatically pickup the 403.html template or return the string 403 Forbidden.
Default manager name 'objects' is deprecated in favor of ModelAdmin.queryset.

This allows use of custom managers and custom querysets.
use PermissionDenied exception in the page request processor example

- In the page request processor example raise a PermisionDenied exception instead of calling the permission_denied view directly.
- Updated the docs for the request processor to mention that if an exception is raised it will be handled like all exceptions are handled in django views.
Merge pull request #473 from adsworth/patch-1

in request_processor example raise PermissionDenied instead of returning HttpResponseForbidden
Merge branch 'master' of git://github.com/josven/feincms into next

* 'master' of git://github.com/josven/feincms:
  Default manager name 'objects' is deprecated in favor of ModelAdmin.queryset.

Conflicts:
	feincms/admin/tree_editor.py