Require a reasonably current DB version on upgrade

This removes support for upgrading the database from very old versions
of MythTV (prior to 0.22).  We haven't made such updates for several
versions, but as the old upgrade code is affected by changes outside our
control (both changes to Qt framework/Qt-MySQL drivers and changes to
MySQL, itself), and because this ancient code is seldom tested with
current versions of external code/programs, we need to limit supported
upgrades to relatively recent upgrades that are testable/supportable.

Users using older versions of MythTV can attempt to upgrade their
existing databases by using intermediate versions of MythTV and attempt
to work through any issues they encounter (even posting questions to the
mythtv-users list).  However, they should understand that upgrading from
very old versions may not work due to things that have changed in the
years since the upgrade code was written and tested.