uploadGeneratetoken: Smarter "create_additional_revision" support

Backported from PR midasplatform#146

This commit improves the support for "create_additional_revision"
introduced in a previous commit. It will not create an additional
revision if last revision has one bitstream and checkum matches

core/controllers/components/ApisystemComponent.php

@@ -379,6 +379,16 @@ function uploadGeneratetoken($args)
           $create_additional_revision = isset($args['create_additional_revision']) ? $args['create_additional_revision'] : false;
           $revision = $itemModel->getLastRevision($item);
 
+          // do not create an additional revision if last revision has one bitstream and checkum matches
+          if($create_additional_revision && $revision)
+            {
+            $bitstreams = $revision->getBitstreams();
+            if (count($bitstreams) == 1 && $args['checksum'] == $bitstreams[0]->getChecksum())
+              {
+              return array('token' => '');
+              }
+            }
+
           if($revision == false || $create_additional_revision)
             {
             // Create new revision if none exists yet or if user explicitly asked for creating a new revision when