(bug 5445) remove autoblocks when user is unblocked

(bug 5445) remove autoblocks when user is unblocked

Previously, whenever we blocked a user, its IP address would be
autoblocked whenever he tries to edit a page. Thus when later unblocking
the username, he would be automatically blocked again if we forgot to
clean up is IP.

This patch introduces a the ipb_parent_block_id column in ipblocks table
to track which block triggered the autoblock command. Thus, when deleting
the original block we can easily remove all subsequentautoblocks.

Schema updaters for MySQL, SQLite and postgres have been added to the
patch but not for the other database types such as ibm_db2, mssql and
Oracle.

Change-Id: I4aa820ae9bbd962a12d0b48b6c638a1b6ff4efc9