matroska: store segment/edition uids in a single structure

To support edition references in matroska chapters, editions need to be
remembered for each chapter and source. To facilitate easier management
of these now-paired uids, a single structure is used.
matroska: parse the requested edition for the segment reference
matroska: set the edition uid when reading a chapter reference
matroska: select the edition using the requested edition uid
matroska: refactor ordered chapter timeline building

This will need to be recursive to support chapters referencing ordered
editions in other files.
matroska: recursively search for referenced segments

When playing a Matroska file with ordered chapters, it may reference
another file by edition uid. When this edition is also ordered, it may
reference other files. When this occurs, the new segment/edition pair is
added to the list of sources to search for.
matroska: support chapter references to ordered editions

Since ordered editions can reference external files, when an ordered
chapter references another ordered edition, we have to go and figure out
what is is referencing as well.
matroska: avoid requesting the same source multiple times
matroska: use memmove when collapsing the source list down
cocoa: fix mouse wheel scrolling
cocoa: refactor precise scrolling to a separate method
libquvi9: work around insane interaction between libquvi and libkdecore

The primary effect of this commit is that it fixes playback resume if
libquvi 0.9 and German locale are used, and libkdecore is on the system.
(See github issue #279.)

libquvi uses libproxy to determine system-wide proxy settings. libproxy
in turn loads libkdecore (if present) to determine KDE proxy settings.
libkdecore has a global constructor, which calls setlocale(LC_ALL, ""),
switching the current locale from "C" to what the user's settings. This
breaks some basic C string processing functions. Note that the locale
won't be set on program start, but only when libproxy calls dlopen() on
its config_kde module, which actually causes libkdecore to be loaded and
initialized.

In particular, with German locale, snprintf() would use "," instead of
"." when formatting float values, which in combination with playback
resume, would lead to parse errors the next time mpv was started, which
is how this issue was found.

I'd consider this a bug with libkdecore or at least libproxy. No library
should ever even touch locale: it might break basic expectations on C
string handling functions, might override program settings, and it's not
thread-safe. But this is so nasty and severe, that a quick hack to fix
it hurts less.

See github issue #279 and KDE bug #325902.
options: --loop=N means playback N times, not N+1 times

The argument or this change is that --loop should set how often the
file is played, not the number of additional repeats.

Based on pull request 277, with additions to the manpage and removal
of "--loop=0".

Signed-off-by: wm4 <wm4@nowhere>
playlist: check for NULL on caller site

Letting some playlist functions randomly accept NULL, while others do
not isn't such a good idea.
command: don't allow changing volume if no audio initialized

Changing volume when audio is disabled was a feature request (github
issue #215), and was introduced with commit 327a779.

But trying to fix github issue #280 (volume is not correct in no-audio
mode, and if audio is re-enabled, the volume set in no-audio mode isn't
set), I concluded that it's not worth the trouble and the current
implementation is questionable all around. (For example, you can't
change the real volume in no-audio mode, even if the AO is open - this
could happen with gapless audio.) It's hard to get right, and the
current mixer code is already hilariously overcomplicated. (Virtually
all of mixer.c is an amalgamation of various obscure corner cases.)

So just remove this feature again.

Note that "options/volume" and "options/mute" still can be used in
idle mode to adjust the volume used next time, though these properties
can't be used during playback and thus not in audio-only mode.

Querying the volume still "works" in audio-only mode, though it can
return bogus values.
command: preferably show "add"/"cycle"/"set" command errors on OSD

Before this, they were shown on terminal only. Now they use the OSD
mechanism, which shows them on the video window or the terminal,
depending on settings and what's available.
cocoa: make --ontop also cover dock+menubar

This only shows any differences when mpv isn't frontmost and is in fullscreen.
Cmd+Tab overlay is still at a higher level as to avoid complete usability fail.
talloc: change talloc destructor signature

Change talloc destructor so that they can never signal failure, and
don't return a status code. This makes our talloc copy even more
incompatible to upstream talloc, but on the other hand this is
preparation for getting rid of talloc entirely.

(The talloc replacement in the next commit won't allow the talloc_free
equivalent to fail, and the destructor return value would be useless.
But I don't want to change any mpv code either; the idea is that the
talloc replacement commit can be reverted for some time in order to
test whether the talloc replacement introduced a regression.)
Replace talloc

There are multiple reasons to do this. One big reason is the license:
talloc is LGPLv3+, which forces mpv to be licensed as GPLv3+.

Another one is that our talloc copy contains modifications, which makes
it essentially incompatible with upstream talloc (in particular, our
version aborts on out of memory conditions - well, it wasn't my idea).
Updating from upstream is also a bit involved - the talloc source is
not really organized in a way to allow copying it into projects (and
this isn't an intended use-case).

Finally, talloc is kind of big and bloated. The replacement halves the
amount of code - mainly because we didn't use all talloc features. It's
even more extreme if you compare upstream talloc (~4700 lines) and the
new allocator without talloc compat (~900 lines).

The replacement provides all features we need. It also doesn't clash
with talloc. (The talloc compatibility wrapper uses macros to avoid
introducing linker-level symbols which could clash with libtalloc.)

It also tries to lower the overhead (only 4 words opposed to 10 words
in talloc for leaf nodes in release mode). Debugging features like leak
reporting can be enabled at compile time and add somewhat more overhead.
Though I'm not sure whether the overhead reduction was actually
successful: allocations with children need an "extra" header, which adds
plenty of overhead, and it turns out that almost half of all allocations
have children. Maybe the implementation could be simplified and the
extra header removed - even then, overhead would be lower than talloc's.

Currently, debugging features can be entirely deactivated by defining
NDEBUG - I'm not sure if anything defines this directly yet, though.

Unlike in talloc, the leak reporting stuff is thread-safe. (That's also
why it's far less elegant, and requires extra list pointers.)

Comes with a compatibility layer, so no changes to mpv source code
are needed. The idea is that we will pretend to be using talloc for
a while, so that we can revert to our old talloc implementation at
any time for debugging purposes.

Some inspiration was taken from Mesa's ralloc:

    http://cgit.freedesktop.org/mesa/mesa/tree/src/glsl/ralloc.h

This is another talloc replacement, but lacks some features we need
(getting size of an allocation, debugging features, being able to
access children in the dtor).

There's some information in ta/README what will happen next and how the
transition is expected to progress.
Copyright, LICENSE: switch to GPL version 2 or later

Now that talloc has been removed, the license can be switched back to
GPLv2+. Actually, there never was a GPLv2+ licensed MPlayer (fork or
not) until now, but removal of some GPLv2-only code makes this possible
now. Rewrite the Copyright file to explain the reasons for the licenses
MPlayer and forks use. The old Copyright file didn't contain anything
interesting anymore, and all information it contained is available at
other places in the source tree.

The reason for the license change itself is that it should improve
interoperability with differently licensed code in general.

This essentially reverts commit 1752808.