[soundcloud] Allow to download tracks marked as not 'streamable'

They use the rtmp protocol but if the are marked as 'downloadable' it can use the direct download link.

test/test_playlists.py

@@ -17,6 +17,7 @@
     DailymotionUserIE,
     VimeoChannelIE,
     UstreamChannelIE,
+    SoundcloudSetIE,
     SoundcloudUserIE,
     LivestreamIE,
     NHLVideocenterIE,
@@ -61,6 +62,14 @@ def test_ustream_channel(self):
         self.assertEqual(result['id'], u'5124905')
         self.assertTrue(len(result['entries']) >= 11)
 
+    def test_soundcloud_set(self):
+        dl = FakeYDL()
+        ie = SoundcloudSetIE(dl)
+        result = ie.extract('https://soundcloud.com/the-concept-band/sets/the-royal-concept-ep')
+        self.assertIsPlaylist(result)
+        self.assertEqual(result['title'], u'The Royal Concept EP')
+        self.assertTrue(len(result['entries']) >= 6)
+
     def test_soundcloud_user(self):
         dl = FakeYDL()
         ie = SoundcloudUserIE(dl)