bug#52737 plugin_dir is set to /usr/local/mysql/lib/plugin while

          starting via mysqld_safe

Rather than hardcode the plugin directory, enhance mysql_config
to fix plugin path when running a relocated install, and use it
to provide the plugin directory to mysqld_safe.

scripts/mysql_config.sh

@@ -88,6 +88,8 @@ pkglibdir_rel=`echo $pkglibdir | sed -e "s;^$basedir/;;"`
 fix_path pkglibdir $pkglibdir_rel lib/mysql lib
 
 plugindir='@pkgplugindir@'
+plugindir_rel=`echo $plugindir | sed -e "s;^$basedir/;;"`
+fix_path plugindir $plugindir_rel lib/mysql/plugin lib/plugin
 
 pkgincludedir='@pkgincludedir@'
 fix_path pkgincludedir include/mysql include

scripts/mysqld_safe.sh

@@ -704,7 +704,7 @@ fi
 
 cmd="`mysqld_ld_preload_text`$NOHUP_NICENESS"
 
-plugin_dir="${PLUGIN_DIR:-$MY_BASEDIR_VERSION/lib/mysql/plugin}${PLUGIN_VARIANT}"
+plugin_dir="${PLUGIN_DIR:-`get_mysql_config --variable=plugindir`}${PLUGIN_VARIANT}"
 
 for i in  "$ledir/$MYSQLD" "$defaults" "--basedir=$MY_BASEDIR_VERSION" \
   "--datadir=$DATADIR" "--plugin-dir=$plugin_dir" "$USER_OPTION"