Issue #1290486 by arthurf: File.mimetypes needs entry for m4v.

includes/file.mimetypes.inc

@@ -373,6 +373,7 @@ function file_default_mimetype_mapping() {
       333 => 'video/vnd.mpegurl',
       347 => 'video/x-flv',
       334 => 'video/x-la-asf',
+      348 => 'video/x-m4v',
       335 => 'video/x-mng',
       336 => 'video/x-ms-asf',
       337 => 'video/x-ms-wm',
@@ -852,6 +853,7 @@ function file_default_mimetype_mapping() {
       'f4a' => 346,
       'f4b' => 346,
       'flv' => 347,
+      'm4v' => 348,
     ),
   );
 }