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/protocol.h

@@ -75,6 +75,7 @@ public:
     return 0;
   }
   virtual bool flush();
+  virtual void end_partial_result_set(THD *thd);
   virtual void prepare_for_resend()=0;
 
   virtual bool store_null()=0;
@@ -173,9 +174,7 @@ public:
 
 void send_warning(THD *thd, uint sql_errno, const char *err=0);
 void net_send_error(THD *thd, uint sql_errno=0, const char *err=0);
-void send_ok(THD *thd, ha_rows affected_rows=0L, ulonglong id=0L,
-	     const char *info=0);
-void send_eof(THD *thd);
+void net_end_statement(THD *thd);
 bool send_old_password_request(THD *thd);
 uchar *net_store_data(uchar *to,const uchar *from, size_t length);
 uchar *net_store_data(uchar *to,int32 from);