Respect allowed file extensions in file mapper.

<?php
hook_feeds_presave{
    //FILE EXTENSION CHECK
    If (isset($entity->field_attachments['und'])){
    //Make list of extensions seperated by a space.
    $extensions = 'rtf doc txt pdf jpg gif png bmp doc docx rtf ppt pptx xls xlsx';
    //Regex adopted from : http://api.drupal.org/api/drupal/includes!file.inc/function/file_validate_extensions/7
    $regex = '/\.(' . preg_replace('/ +/', '|', preg_quote($extensions)) . ')$/i';
    //Loop through array of file field, if match unset from array and delete file
    foreach ($entity->field_attachments['und'] as $k => $v){
        if (!preg_match($regex, $v['filename'])) {
            $file = file_load($v['fid']);
            unset($entity->field_attachments['und'][$k]);
            file_delete($file, $force = FALSE);
         }
     }
    }
?>

<?php
$entity->body["und"][0]["value"] = $entity->body["und"][0]["value"] ."\n" .'Attachment ' .$v['filename'] .' was removed, only the following extensions are allowed: ' .$extensions;
?>