Autocomplete broken in Drupal 7.39

FeyP's patch fixes the issue for me.
Thank you!

The first part of the patch looks good, but I think the second part is unnecessary. The value callback doesn't have anything to do with the Ajax system, and either way I don't think this module would have any reason to set the verification header on its own?

Here's a version that just includes the first part. Works fine for me.

I will add this to the Drupal 7.39 release notes.

Patch from #5 works for me. - Thanks!

Here's a quick one if you don't want to patch the module: just implement hook_element_info_alter() in a custom module!

function mymodule_element_info_alter(&$type) {
  $type['entityreference']['#process'] = array(
    'entityreference_autocomplete_process_entityreference',
    'form_process_autocomplete',
    'ajax_process_form'
  );
}

I think #5 is going to cause a fatal error on 7.38 so it seems that either a dependency on >=7.39 or a function_exists() is needed.

Thanks everybody for the ideas and suggested patches. As it's been pointed out, there's a need for the dependency in the .info file, or the function_exists check.

I've solved this with merging the 2 patches provided in #2561431: Elements with autocomplete require #autocomplete_input since Drupal core 7.39., which is a duplicate of this (it was created after this one), but used it because the function_exists check was provided already in one of the patches there.

So, fixed now in dev, and rolling out a new release now. Thanks all \o/.