Ticket #4816 - File uploader doesn't accept m4a files.

inc/js/classes/BxDolUploader.js

@@ -382,7 +382,7 @@ BxDolUploaderBase.prototype.getMimeTypefromString  = function (ext) {
         'movie'  : 'video/x-sgi-movie',
         'mp2'    : 'audio/mpeg',
         'mp3'    : 'audio/mpeg',
-        'm4a'    : 'audio/mp4',
+        'm4a'    : ['audio/mp4', 'audio/x-m4a'],
         'mp4'    : 'video/mp4',  
         'm4v'    : 'video/mp4', 
         'mpa'    : 'video/mpeg',