mariadb-common.preinst: undo my.cnf symlink and my.cnf.old from the fallback

to prepare clean migration to a symlink managed with
/usr/share/mysql-common/configure-symlinks

the same code is part of mysql-common.preinst to ensure this cleanup is
performed by the first package being unpacked

debian/changelog

@@ -4,6 +4,7 @@ mariadb-10.0 (10.0.20-3) UNRELEASED; urgency=medium
   * mariadb-common: Depend on a version of mysql-common that ships
     /usr/share/mysql-common/configure-symlinks.  (Closes: #787533)
   * mariadb-common.postinst: Drop fallback my.cnf symlink management.
+  * mariadb-common.preinst: Clean up my.cnf/my.cnf.old from the fallback.
 
  -- Andreas Beckmann <anbe@debian.org>  Wed, 08 Jul 2015 09:09:58 +0200
 

debian/mariadb-common.preinst

+#!/bin/sh
+set -e
+
+if [ "$1" = "install" ] || [ "$1" = "upgrade" ]; then
+    if dpkg --compare-versions "$2" lt-nl "10.0.20-3~" ; then
+
+        # revert fallback my.cnf symlink setup performed by mariadb-common
+        # from 10.0.17-1~exp2 upto 10.0.20-2
+        if [ -L /etc/mysql/my.cnf ] && [ -f /etc/mysql/my.cnf.old ]; then
+            if [ "$(readlink /etc/mysql/my.cnf)" = "mariadb.cnf" ]; then
+                echo "Reverting my.cnf -> mariadb.cnf symlink setup by mariadb-common"
+                rm /etc/mysql/my.cnf
+                mv /etc/mysql/my.cnf.old /etc/mysql/my.cnf
+            fi
+        fi
+
+    fi
+fi
+
+#DEBHELPER#