playbin: rename GType of stream selector pad to avoid clash with input-selector from -bad

Rename the GType of the pads of playbin's internal stream selector
element so they don't use the same type name as input-selector's
pads. Fixes #589622.

gst/playback/gststreamselector.c

@@ -143,7 +143,7 @@ gst_selector_pad_get_type (void)
     };
 
     selector_pad_type =
-        g_type_register_static (GST_TYPE_PAD, "GstSelectorPad",
+        g_type_register_static (GST_TYPE_PAD, "GstPlaybinSelectorPad",
         &selector_pad_info, 0);
   }
   return selector_pad_type;