administration: fix MissingCategoryDocumentConstraint with acquisition
MissingCategoryDocumentConstraint was incorrectly using unrestrictedTraverse, unlike category API which uses its own resolveCategory method with better semantics. Because of this, some problems were not reported: - categories using paths that resolve by acquisition, but does not exists as such (like in the test) - categories using path with dynamic objects, like a website language. /reviewed-on !986