plugins radiocol, xep-0054: better handling of upload errors:

- radiocolSongAdded is now asynchronous
- _buildAvatar return a Failure if the image is not readable

src/plugins/plugin_xep_0054.py

@@ -23,6 +23,7 @@ from twisted.internet.defer import inlineCallbacks, returnValue
 from twisted.words.protocols.jabber import jid
 from twisted.words.protocols.jabber.xmlstream import IQ
 from twisted.words.xish import domish
+from twisted.python.failure import Failure
 import os.path
 
 from zope.interface import implements
@@ -236,7 +237,7 @@ class XEP_0054(object):
         try:
             img = Image.open(filepath)
         except IOError:
-            raise exceptions.DataError("Can't open image")
+            return Failure(exceptions.DataError("Can't open image"))
 
         if img.size != (64, 64):
             img = img.resize((64, 64))