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.