Prevent soundcloud from downloading existing episodes each update.

GUIDs are stored in the database as strings, but soundcloud creates them
as integers. Python no longer succeeds when comparing these integers to
the string keys from the existing database entries. This produces new
episodes on every update which then collide with the existing GUIDs.

src/gpodder/plugins/soundcloud.py

@@ -153,7 +153,7 @@ class SoundcloudUser(object):
                     'url': url,
                     'file_size': int(filesize),
                     'mime_type': filetype,
-                    'guid': track.get('permalink', track.get('id')),
+                    'guid': str(track.get('permalink', track.get('id'))),
                     'published': soundcloud_parsedate(track.get('created_at', None)),
                 }
         finally: