feature #509 summarize history more often

Every 1000 log entry inserted, Piwigo performs an history summarize.

The summarize process has also been optimized: no longer used column
history.summarized (no longer need to update it, which took a lot in time),
we now save the history_id_from and history_id_to in history_summary table.
This way we know from where to start on next summarize.

For now, for a simple performance reason, we keep column history.summarized,
because removing it may take a long time on huge tables. Once we will have
automatic purge on history, it will be safer to drop this column.

include/functions.inc.php

@@ -495,6 +495,13 @@ INSERT INTO '.HISTORY_TABLE.'
 ;';
   pwg_query($query);
 
+  $history_id = pwg_db_insert_id(HISTORY_TABLE);
+  if ($history_id % 1000 == 0)
+  {
+    include_once(PHPWG_ROOT_PATH.'admin/include/functions_history.inc.php');
+    history_summarize(50000);
+  }
+
   return true;
 }