Prevent save on automatic updates, if content has not changed

If content is auto updated and linkchecker is not able to replace the link, the bundle is nevertheless saved as new revision with change notice without any content changes.

This can currently only happen if the urls in content are relative (../foo/../bar/) or absolute (/foo/bar). Full qualified urls are not affected at all, also not with html entities inside.

It looks somehow difficult to track these differences with fields and there is no object_diff() in php. A possible and fast solution may be creating a json representation of the objects with drupal_json_encode() before and after string replacements to compare them and if they do not match only a changed object can be saved. If the json result string may be too long we can hash them to compare.