Protect private wikis by providing basic read restrictions,
closely following the example of the action API.
The BasicAccess module provides a narrow interface for this
functionality, without exposing the whole session/user concept to the
router.
Also, add RouterTest and fix a bug in Router::getRelativePath() thus
discovered.
Change-Id: I82319d56f08b2eec4a585ff6dbd348ccdbadc5b5
