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().

include/mysql_com.h

@@ -203,14 +203,10 @@ typedef struct st_net {
   unsigned int *return_status;
   unsigned char reading_or_writing;
   char save_char;
-  my_bool no_send_ok;  /* For SPs and other things that do multiple stmts */
+  my_bool unused0; /* Please remove with the next incompatible ABI change. */
   my_bool unused; /* Please remove with the next incompatible ABI change */
   my_bool compress;
-  /*
-    Set if OK packet is already sent, and we do not need to send error
-    messages
-  */
-  my_bool no_send_error;
+  my_bool unused1; /* Please remove with the next incompatible ABI change. */
   /*
     Pointer to query object in query cache, do not equal NULL (0) for
     queries in cache that have not stored its results yet
@@ -221,11 +217,14 @@ typedef struct st_net {
     functions and methods to maintain proper locking.
   */
   unsigned char *query_cache_query;
-  unsigned int last_errno;
-  unsigned char error;
-  my_bool report_error; /* We should report error (we have unreported error) */
+  unsigned int client_last_errno;
+  unsigned char error; 
+  my_bool unused2; /* Please remove with the next incompatible ABI change. */
   my_bool return_errno;
-  char last_error[MYSQL_ERRMSG_SIZE], sqlstate[SQLSTATE_LENGTH+1];
+  /** Client library error message buffer. Actually belongs to struct MYSQL. */
+  char client_last_error[MYSQL_ERRMSG_SIZE];
+  /** Client library sqlstate buffer. Set along with the error message. */
+  char sqlstate[SQLSTATE_LENGTH+1];
   void *extension;
 } NET;