Updated mediawiki/extensions
Project: mediawiki/extensions/UserMerge  d77648cff1eccefd019e0f78ad5a254e0b799435

Add initial tests for MergeUser

For some reason they don't pass when @group Database
is added and uses the cloned database, so I left
that as @todo to be fixed later.

Change-Id: Ia275e3ca840ca8ec9e46d0dde8cc3b3f3be002f0