taglist: add a tag for midi base note numbers

Audio files containing sampled instruments can have metadata describing the note
that was played on the instrument.
taglist: fix since-marker in docs (we're in 1.3.X)
taglist: fix since marker again (1.3 -> 1.4)

Since markers should point to the appropriate stable version.
nettimeprovider: Remove dead code

err is always NULL by the point we reach this line

COVERITY CID 1037151
queue: Remove unneeded checks

item is guaranteed to be non-null.

COVERITY CID 1037152
COVERITY CID 1037153
Revert "nettimeprovider: Remove dead code"

This reverts commit 9649cd4ca19a75d0319117a77a7609e4b8c96533.

This is not right, and it's also not what coverity
is complaining about.
nettimeprovider: remove unnecessary NULL check

Error is never NULL when we break out of the loop.

COVERITY CID 1037151
pad: Only call IDLE probes if we are actually idle

Also only check the data types for non-IDLE probes. When we
are idle, we have no data type obviously.

Previously we were calling IDLE probes during data flow whenever
a non-blocking probe would be called. The pad was usually not idle
at that time.
pad: Keep an extra ref of the pad when calling an IDLE probe immediately

The callback might destroy the pad.
tee: Keep another ref to our one and only srcpad around while pushing

A pad probe on that pad might otherwise just release the pad, drop
the last reference and cause great misery.

https://bugzilla.gnome.org/show_bug.cgi?id=721300
tee: Remove dyn lock

It was used for pad-alloc in 0.10 but currently is completely unused
and not necessary. All pad access is protected by the tee object lock
and keeping another reference to the current pad.
pad: Check if new probes need to be called when adding/removing some

This allows blocking a pad, add a new blocking probe, removing
the first probe and then having the second probe called. Which
could then decide that data-flow should actually continue
instead of blocking now.

https://bugzilla.gnome.org/show_bug.cgi?id=721289
pad: Add unit test for adding/removing blocking probes while a pad is blocked

And make sure that these new probes are actually called if they should
instead of silently blocking the pad forever.

https://bugzilla.gnome.org/show_bug.cgi?id=721289
design/part-toc.txt: update design docs
baseparse: refactor pending events pushing

Refactor code repeated 3 times to a common function

https://bugzilla.gnome.org/show_bug.cgi?id=721350
baseparse: push pending events before GAP event

A GAP event is handled as an empty buffer by sinks and they expect
to receive start up events before GAP events (like a segment).

This is important specially if there is a GAP at the beginning of
a stream (before any buffers) so that the segment event can be
pushed downstream before the GAP

https://bugzilla.gnome.org/show_bug.cgi?id=721350
baseparse: remove pending_segment as it was being misused

It wasn't required, instead baseparse was using it to check the media
caps to identify if it was handling audio or video.

The pending_segment was removed and a checked_media boolean
replaced it for a more accurate naming.

https://bugzilla.gnome.org/show_bug.cgi?id=721350
multiqueue: Fix hanging if shut down while handling a serialized query

https://bugzilla.gnome.org/show_bug.cgi?id=721253