Updated mediawiki/extensions
Project: mediawiki/extensions/UserMerge  178259a9086b4ebd694c56621f9283b928c4e4cb

Rename special page class and file to match current conventions

UserMerge --> SpecialUserMerge
UserMerge_body.php --> SpecialUserMerge.php

Change-Id: I3c61e77e892e83f97e0dff8b9127b3e24ae7cb46