Merged the fix for bug #11936829 to 5.5.11 release

Bug #11936829: DIFF. BETWEEN MYSQL.USER (AUTHENTICATION_STRING) IN 
  FRESH AND UPGRADED 5.5.11
             
There was no modification for pre 5.5.11 builds that had 
authentication_string.  Thus the column was not upgraded 
by mysql_upgrade.
                         
Fixed by adding an ALTER TABLE MODIFY to update an existing 
column to the latest type version.
                                     
Test suite added.

mysql-test/r/plugin_auth.result

@@ -400,4 +400,51 @@ ORDER BY COLUMN_NAME;
 IS_NULLABLE	COLUMN_NAME
 YES	authentication_string
 YES	plugin
+#
+# Bug #11936829: diff. between mysql.user (authentication_string) 
+#   in fresh and upgraded 5.5.11
+#
+SELECT IS_NULLABLE, COLUMN_NAME FROM INFORMATION_SCHEMA.COLUMNS
+WHERE TABLE_SCHEMA= 'mysql' AND TABLE_NAME= 'user' AND
+COLUMN_NAME IN ('plugin', 'authentication_string')
+ORDER BY COLUMN_NAME;
+IS_NULLABLE	COLUMN_NAME
+YES	authentication_string
+YES	plugin
+ALTER TABLE mysql.user MODIFY plugin char(64) DEFAULT '' NOT NULL;
+ALTER TABLE mysql.user MODIFY authentication_string TEXT NOT NULL;
+Run mysql_upgrade on a 5.5.10 external authentication column layout
+mtr.global_suppressions                            OK
+mtr.test_suppressions                              OK
+mysql.columns_priv                                 OK
+mysql.db                                           OK
+mysql.event                                        OK
+mysql.func                                         OK
+mysql.general_log                                  OK
+mysql.help_category                                OK
+mysql.help_keyword                                 OK
+mysql.help_relation                                OK
+mysql.help_topic                                   OK
+mysql.host                                         OK
+mysql.ndb_binlog_index                             OK
+mysql.plugin                                       OK
+mysql.proc                                         OK
+mysql.procs_priv                                   OK
+mysql.proxies_priv                                 OK
+mysql.servers                                      OK
+mysql.slow_log                                     OK
+mysql.tables_priv                                  OK
+mysql.time_zone                                    OK
+mysql.time_zone_leap_second                        OK
+mysql.time_zone_name                               OK
+mysql.time_zone_transition                         OK
+mysql.time_zone_transition_type                    OK
+mysql.user                                         OK
+SELECT IS_NULLABLE, COLUMN_NAME FROM INFORMATION_SCHEMA.COLUMNS
+WHERE TABLE_SCHEMA= 'mysql' AND TABLE_NAME= 'user' AND
+COLUMN_NAME IN ('plugin', 'authentication_string')
+ORDER BY COLUMN_NAME;
+IS_NULLABLE	COLUMN_NAME
+YES	authentication_string
+YES	plugin
 End of 5.5 tests

mysql-test/t/plugin_auth.test

@@ -490,4 +490,26 @@ SELECT IS_NULLABLE, COLUMN_NAME FROM INFORMATION_SCHEMA.COLUMNS WHERE
   TABLE_SCHEMA='mysql'
 ORDER BY COLUMN_NAME;
 
+
+--echo #
+--echo # Bug #11936829: diff. between mysql.user (authentication_string) 
+--echo #   in fresh and upgraded 5.5.11
+--echo #
+
+SELECT IS_NULLABLE, COLUMN_NAME FROM INFORMATION_SCHEMA.COLUMNS
+  WHERE TABLE_SCHEMA= 'mysql' AND TABLE_NAME= 'user' AND
+    COLUMN_NAME IN ('plugin', 'authentication_string')
+  ORDER BY COLUMN_NAME;
+ALTER TABLE mysql.user MODIFY plugin char(64) DEFAULT '' NOT NULL;
+ALTER TABLE mysql.user MODIFY authentication_string TEXT NOT NULL;
+
+--echo Run mysql_upgrade on a 5.5.10 external authentication column layout
+--exec $MYSQL_UPGRADE --skip-verbose --force 2>&1
+
+SELECT IS_NULLABLE, COLUMN_NAME FROM INFORMATION_SCHEMA.COLUMNS
+  WHERE TABLE_SCHEMA= 'mysql' AND TABLE_NAME= 'user' AND
+    COLUMN_NAME IN ('plugin', 'authentication_string')
+  ORDER BY COLUMN_NAME;
+
+
 --echo End of 5.5 tests

scripts/mysql_system_tables_fix.sql

@@ -642,6 +642,7 @@ drop procedure mysql.die;
 
 ALTER TABLE user ADD plugin char(64) DEFAULT '',  ADD authentication_string TEXT;
 ALTER TABLE user MODIFY plugin char(64) DEFAULT '';
+ALTER TABLE user MODIFY authentication_string TEXT;
 
 -- Need to pre-fill mysql.proxies_priv with access for root even when upgrading from
 -- older versions