Merge with MySQL 5.1, with following additions:

- Moved some code from innodb_plugin to xtradb, to ensure that all tests runs
- Did changes in pbxt and maria storage engines becasue of changes in thd->query
- Reverted wrong code in sql_table.cc for how ROW_FORMAT is used.

This is a re-commit of Monty's merge to eliminate an extra commit from
MySQL-5.1.42 that was accidentally included in the merge.

This is a merge of the MySQL 5.1.41 clone-off (clone-5.1.41-build). In
case there are any extra changes done before final MySQL 5.1.41
release, these will need to be merged later before MariaDB 5.1.41
release.

libmysqld/lib_sql.cc

@@ -142,6 +142,8 @@ emb_advanced_command(MYSQL *mysql, enum enum_server_command command,
   if (!skip_check)
     result= thd->is_error() ? -1 : 0;
 
+  thd->mysys_var= 0;
+
 #if defined(ENABLED_PROFILING) && defined(COMMUNITY_SERVER)
   thd->profiling.finish_current_query();
 #endif
@@ -634,6 +636,7 @@ void *create_embedded_thd(int client_flag)
 
   thread_count++;
   threads.append(thd);
+  thd->mysys_var= 0;
   return thd;
 err:
   delete(thd);