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/opt_range.cc

@@ -1271,7 +1271,7 @@ int QUICK_RANGE_SELECT::init_ror_merged_scan(bool reuse_handler)
       the storage engine calls in question happen to never fail with the 
       existing storage engines. 
     */
-    thd->net.report_error= 1; /* purecov: inspected */
+    my_error(ER_OUT_OF_RESOURCES, MYF(0)); /* purecov: inspected */
     /* Caller will free the memory */
     goto failure;  /* purecov: inspected */
   }