Bug#12713 "Error in a stored function called from a SELECT doesn't

cause ROLLBACK of statement", part 1. Review fixes.

Do not send OK/EOF packets to the client until we reached the end of 
the current statement.
This is a consolidation, to keep the functionality that is shared by all 
SQL statements in one place in the server.
Currently this functionality includes:
- close_thread_tables()
- log_slow_statement().

After this patch and the subsequent patch for Bug#12713, it shall also include:
- ha_autocommit_or_rollback()
- net_end_statement()
- query_cache_end_of_result().

In future it may also include:
- mysql_reset_thd_for_next_command().

sql/sql_db.cc

@@ -921,6 +921,8 @@ bool mysql_rm_db(THD *thd,char *db,bool if_exists, bool silent)
     {
       ha_drop_database(path);
       query_cache_invalidate1(db);
+      (void) sp_drop_db_routines(thd, db); /* @todo Do not ignore errors */
+      Events::drop_schema_events(thd, db);
       error = 0;
     }
   }
@@ -956,6 +958,7 @@ bool mysql_rm_db(THD *thd,char *db,bool if_exists, bool silent)
       /* These DDL methods and logging protected with LOCK_mysql_create_db */
       mysql_bin_log.write(&qinfo);
     }
+    thd->clear_error();
     thd->server_status|= SERVER_STATUS_DB_DROPPED;
     send_ok(thd, (ulong) deleted);
     thd->server_status&= ~SERVER_STATUS_DB_DROPPED;
@@ -999,8 +1002,6 @@ bool mysql_rm_db(THD *thd,char *db,bool if_exists, bool silent)
   }
 
 exit:
-  (void)sp_drop_db_routines(thd, db); /* QQ Ignore errors for now  */
-  Events::drop_schema_events(thd, db);
   /*
     If this database was the client's selected database, we silently
     change the client's selected database to nothing (to have an empty