Changed some DatabaseBase type hints to IDatabase

Change-Id: I1158c71f110b140473f56d5cbe352da1f4513ad9
Make maintenance/findHooks.php check includes/mail/

bf8810d6bcba81de0452ef46963e46d128ea41f2 split some
email-related code into a separate directory, along
with references to five hooks, thus listed as
'Documented and not found':
* AbortTalkPageEmailNotification
* AlternateUserMailer
* SendWatchlistEmailNotification
* UpdateUserMailerFormattedPageStatus
* UserMailerChangeReturnPath

Change-Id: I7601ea2f2b0c4c9dcf802114e464be9af88fa5cb
Merge "Changed some DatabaseBase type hints to IDatabase"