These messages can be confusing, but they are not critical.

This replaces the old `dead` flag which was unreliable; it was `false`
if the EventThread was not yet started, which could cause deadlocks in
BlockingCall().

Since we switched from autotools to Meson in commit
94592c14, we don't need to include
`config.h` early to properly enable large file support.  Meson passes
the required macros on the compiler command line instead of defining
them in `config.h`.

This means we can include `config.h` at any time, whenever we want to
check its macros, and there are no ordering constraints.

MPD's default is 100ms, which is too long for the real-time I/O
thread.  The OutputThread has 100us, but the real-time I/O thread
might have tighter deadlines.

This change has currently no effect (I believe), because nobody uses
timers on the RTIO thread.

The normal I/O event thread can have a large latency, e.g. when
libgnutls loads all TLS CA certificates for a https connect.  This
makes it unreliable for the ALSA I/O notifications, and causes ring
buffer xruns.  To avoid interfering with high latency events such as
CURL's, we move the ALSA I/O events to a separate I/O thread which
also obtains real-time scheduling (if possible).

Closes #221

We don't need to access Thread::handle early inside the EventThread,
so we don't need this trick anymore.

Allocate a decoder_control object where needed, and pass it around.
This will allow more than one decoder thread one day.

This updates the copyright header to all be the same, which is
pretty much an update of where to mail request for a copy of the GPL
and the years of the MPD project. This also puts all committers under
'The Music Player Project' umbrella. These entries should go
individually in the AUTHORS file, for consistancy.

"LOG_H" is a macro which is also used by ffmpeg/log.h.  This is
ffmpeg's fault, because short macros should be reserved for
applications, but since it's always a good idea to choose prefixed
macro names, even for applications, we are going to do that in MPD.

It should be obvious in which thread or context a function is being
executed at runtime.  The code which was left in decode.c is for the
decoder thread itself; give the file a better name.

This is the last of the three variables.  Now we don't need
playerData.h anymore in most sources.

This releases several include file dependencies.  As a side effect,
"CHUNK_SIZE" isn't defined by decoder_api.h anymore, so we have to
define it directly in the plugins which need it.  It just isn't worth
it to add it to the decoder plugin API.

Now that "dc" is available here, we don't have to pass it to
decoder_is_idle() and decoder_is_starting() anymore.

Include only headers which are really required.  This speeds up
compilation and helps detect cross-layer accesses.

git-svn-id: https://svn.musicpd.org/mpd/trunk@7372 09075e82-0dd4-0310-85a5-a0d7c8717e4f