Fix for BUG#37873 "Client gets ok from INSERT VALUES before commit record is on disk":

this was true also for INSERT SELECT, UPDATE, DELETE. This fix will be removed when Maria supports COMMIT/ROLLBACK
("Maria 2.0"), because then Maria will trans_register_ha() and so participate in ha_commit_trans().
Without the fix, the assertion added to ha_maria::external_lock() fires many times in *maria*.test.

sql/sql_parse.cc:
  Before sending OK to client, commit transaction in Maria.
storage/maria/ha_maria.cc:
  Assertion added to external_lock() when committing: OK should not have been sent yet (ACI*D*).
  In ha_maria::implicit_commit(), possibility to not create a new transaction, this is used
  before net_end_statement(), when the next step is close_thread_tables();
  in this use case, ha_maria::implicit_commit() should not commit if under LOCK TABLES.
storage/maria/ha_maria.h:
  new prototype

sql/sql_parse.cc

@@ -127,7 +127,7 @@ bool end_active_trans(THD *thd)
     if (ha_commit(thd))
       error=1;
 #ifdef WITH_MARIA_STORAGE_ENGINE
-    ha_maria::implicit_commit(thd);
+    ha_maria::implicit_commit(thd, TRUE);
 #endif
   }
   thd->options&= ~(OPTION_BEGIN | OPTION_KEEP_LOG);
@@ -1132,6 +1132,10 @@ bool dispatch_command(enum enum_server_command command, THD *thd,
     {
       char *beginning_of_next_stmt= (char*) end_of_stmt;
 
+#ifdef WITH_MARIA_STORAGE_ENGINE
+      ha_maria::implicit_commit(thd, FALSE);
+#endif
+
       net_end_statement(thd);
       query_cache_end_of_result(thd);
       /*
@@ -1496,6 +1500,10 @@ bool dispatch_command(enum enum_server_command command, THD *thd,
     thd->mysys_var->abort= 0;
   }
 
+#ifdef WITH_MARIA_STORAGE_ENGINE
+  ha_maria::implicit_commit(thd, FALSE);
+#endif
+
   net_end_statement(thd);
   query_cache_end_of_result(thd);