[Backport] Support for methods on User model when checking permissions

The ``permissions_required`` decorator, and hence
``Application.permissions_map`` and
``Application.default_permissions``, now
handle both methods and properties on the User model.
Previously, it
wasn't supported, but a docstring showed
``is_anonymous`` as an example,
which is a method.

Cherry-picked from 8b610f66cd79b38f2a12509a44f37490117f6267
Bump version to 0.6.5 and update docs
Merge branch 'releases/0.6'

Conflicts:
	docs/source/releases/index.rst
	oscar/__init__.py