Maintenance script to clean up mismatched user names in ipblocks

For blocks with ipb_user non-zero, the ipb_address field is supposed to
match user_name. But due to various bugs over the years, this doesn't
hold true.

Due to those old bugs, we also have rows with the same ipb_user (and
ipb_auto and ipb_anon_only, since those only apply to IP blocks) but
different ipb_address. Those also need cleaning up, both to prevent
a unique constraint violation and to stop errors in ApiQueryAllUsers.

Bug: 34014
Bug: 72560
Change-Id: I519078ec011dbd0043811a78c3f913792a4df7fe
(cherry picked from commit 0a32c179e49085dd6b6c0ef3111497229f4fa10f)