Remove "\\" in namespacing. This is a Doxygen compatibility hack but
does not seem needed anymore, Doxygen reads namespaced class names
correctly, see e.g. https://doc.wikimedia.org/mediawiki-core/master/php/classMediaWiki_1_1Services_1_1ServiceContainer.html
PHP IDEs, on the other hand, were broken by the double backslash.
As an unrelated small doc fix, add parameter docs to PermissionError
constructor (parent has different arguments so the inherited
documentation is wrong).
Change-Id: I6da0f512b8c84f65fd20e90e4617108fe6a8fcd2
4085db348e