ext/gio/: Improve debugging a bit.

ext/gio/: Improve debugging a bit.

Original commit message from CVS:
* ext/gio/gstgiobasesink.c: (close_stream_cb):
* ext/gio/gstgiobasesrc.c: (close_stream_cb):
Improve debugging a bit.
* ext/gio/gstgiosink.c: (mount_cb), (gst_gio_sink_start):
* ext/gio/gstgiosink.h:
* ext/gio/gstgiosrc.c: (mount_cb), (gst_gio_src_start):
* ext/gio/gstgiosrc.h:
Try to mount the enclosing volume of a GFile if it isn't mounted
yet. This requires us to wait for an async operation to finish, done
with an nested GMainLoop. Authentication is not supported yet, will
come later.