gst/elements/: Beautify 'last-message' output: print 'none' for buffer timestamps and durations if none is set; impro...

Original commit message from CVS:
* gst/elements/gstfakesink.c: (gst_fake_sink_render):
* gst/elements/gstfakesrc.c: (gst_fake_src_create):
Beautify 'last-message' output: print 'none' for buffer timestamps
and durations if none is set; improve alignment with next messages.