streams with non-TIME segments will not have timestamps ...
... and therefore will never unblock the other streams.

Fixes blocking issue when using playbin suburi feature

Don't align the palette data. Fixes endless loop when trying to align
paletted formats.

Only make the navigation event writable when we need to change it.

It needs to be reworked for 1.0

When we are operating in pull mode, we need to pull from upstream and push
downstream. Also make sure to push tags first.

... and clean up some related resolved FIXMEs

Only provide a clock when we are not flushing, this means that we have posted a
PROVIDE_CLOCK message. We used to check if we were acquired but that doesn't
work anymore now that we do the negotiation async in the streaming thread: it's
possible that we are still negotiating when the pipeline asks us for a clock.

Make it possible for subclasses to provide the timestamp (as an absolute time
against the pipeline clock) of the last read data.
Fix up alsa to provide the timestamp received from alsa. Because the alsa
timestamps are in monotonic time, we can only do this when the monotonic clock
has been selected as the pipeline clock.

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=635256

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=683672

But we should only do that if it comes straight from a
container or wavparse, not if it comes from a decoder,
otherwise it's probably not really meaningful.

It's all been ported to the latest GLib API now.

Instead of home-grown solution.

People expect audiorate to fix things up and not make things worse
by default, so let's default to a similar tolerance as audiosinks
do. Should help with transcoding and the like, though one might
possible still want higher values then.