Allow disabling of file extension checks

It looks like currently we cannot disable extension checks. Changing this would break current default behaviour.

There is, however, 7.x-2.x branch, where we plan to rewrite the module and include changes like this.

I was able to remove file extension check when using IMCE by placing the following code in a custom module:
(replace MYMODULE with the name of your custom module)

/**
 * Implements hook_element_info_alter().
 */
function MYMODULE_element_info_alter(&$type) {
  if (isset($type['plupload'])) {
    $type['plupload']['#process'][] = 'MYMODULE_plupload_element_process';
  }
}

/**
 * Process plupload element.
 */
function MYMODULE_plupload_element_process($element) {
  // Remove extension validation if using IMCE.
  if (isset($element['#upload_validators']['imce_validate_all'])) {
    unset($element['#upload_validators']['file_validate_extensions']);
  }
  return $element;
}

The hook implementation didn't work for me, but the attached patch does.

It's a simple patch to remove the default list of file extensions. This removed them from the process function and validation. In practice this will fall back to using the file extensions list from the file field in question, but as above, if that list is empty, then that should be honoured by this code, especially since plupload itself has supported this since https://github.com/moxiecode/plupload/commit/57400ddea4aa20c94944ef1c28d...

I know this may break expected defaults so understand why it may not be committed. But I think the file fields already have a default set of file extensions and unless you do something to allow that list to be empty, the defaults set in this module will never be applied.