play: Update buffering state for live pipelines

Update the buffering variable, even for live pipelines so that we don't
print \n for each buffering message.
play: Improve pipeline states

First set the pipeline to the PAUSED state to check if we are dealing
with a live pipeline or not. Then move to the desired state.

If we don't do this, it is possible that we receive a BUFFERING message
before we know that the pipeline is live and we would set the pipeline
to PAUSED and deadlock.
tag: exif: avoid adding empty strings

Fixes assertion with some jpeg files
audioresample: Don't left-shift into the sign bit, instead use unsigned integers
audiodecoder: Plug caps leaks

We were returning in various places without unreffing the caps, and
we were also leaking (overwriting) the caps we got from _get_current_caps()

Spotted by Haakon Sporsheim in #gstreamer
giobasesink: Implement handling of the SEEKING query
docs: remove outdated and pointless 'Last reviewed' lines from docs

They are very confusing for people, and more often than not
also just not very accurate. Seeing 'last reviewed: 2005' in
your docs is not very confidence-inspiring. Let's just remove
those comments.
playbin: add nick for soft colorbalance play flag to fix gst-inspect

Fix gst-inspect-1.0 playbin criticals when printing the
flags, which was caused by a missing nick name for one
of the flags.
giobasesink: we mustn't change the format of a query response

Not even in the DEFAULT case. That's bad 0.10 behaviour, no caller
is ever going to check the format of the response.