I got this PHP notice with ConfirmAccount 0d79eb3 + MW 1.29alpha + PHP 7.0:
Only variables should be assigned by reference in backend/ConfirmAccount.class.php on line 217
The faulty syntax is:
$magic =& MimeMagic::singleton();
When searching in MediaWiki codebase elsewhere for MimeMagic, the usual usage is $magic = MimeMagic::singleton();.