Check for an existing MySQL server package from a different vendor or
major MySQL version. In such a case, refuse to install the server and
recommend how to safely remove the old packages before installing the
new ones.
support-files/mysql.spec.sh:
Add to the %pre server scriptlet checks to ensure that we're not
upgrading from another vendor's package, or that this is not a
major version upgrade. If an automatic upgrade isn't safe, print
basic instructions on how to do a manual upgrade, and bail out.