* Instead of using "set foreign_key_checks=0" before
altering voicemail_spool voicemail_users tables the
foreign key voicemail_spool.`v_s_mailboxuser_ref` is
dropped instead and re-created after the alter table operations
(same lines where "set foreign_key_checks=0" and "set
foreign_key_checks=1" were respectively.
* That addresses the changed behavior with MariaDB 10.11.6
where "alter table" statements the change columns involved
in a foreign key and potentially causing data loss are prohibited
even with "set foreign_key_checks=0".
* This change is only valid for new deployments and databases
with already applied 6425.up are not affected.
Change-Id: I2f2a85ca9f9f7d15058f41f5d8eaaec23ec501fa
Kirill Solomko