This eliminates some overhead, because the compiler doesn't need to
consider these functions throwing.

Add the new idle event to Idle.hxx/Idle.cxx.

Implements the error checks missing in commit 0bad8406

This commit adds the NeighborPlugin API which can be used to detect
nearby file servers that can be used by input plugins.  This list of
servers is exported using the new "listneighbors" command.  The idle
even "neighbor" notifies interested clients when a new neighbor is
found or an existing one is lost.

There's a lot missing currently: protocol&user documentation, and a
way to "mount" remote servers into the music database.  Obviously,
some code from the UPnP database plugin can be moved to a neighbor
plugin.

Some clients have visual feedback for "database update is running".
Using the "database" idle event is unreliable, because it is only
emitted when the database was actually modified.  This patch adds the
"update" event, which is emitted when the update is started, and again
when the update is finished, disregarding whether it has been
modified.

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.

The client may provide the names of idle events as arguments to the
"idle" command to inform MPD that it is only interested in these
events.

"idle" waits until something noteworthy happens on the server,
e.g. song change, playlist modified, database updated.  This allows
clients to keep up to date without polling.

"bool" should be used in C99 programs for boolean values.

When there are standardized headers, use these instead of the bloated
os_compat.h.

Typedefs shouldn't be used, use the bare struct names instead.

There was a known deadlocking bug in the notify library: when the
other thread set notify->pending after the according check in
notify_wait(), the latter thread was deadlocked.  Resolve this by
synchronizing all accesses to notify->pending with the notify object's
mutex.  Since notify_signal_sync() was never used, we can remove it.
As a consequence, we don't need notify_enter() and notify_leave()
anymore; eliminate them, too.

With the macro NOTIFY_INITIALIZER, you can statically initialize a
notify object.

Destroy the mutex when it is not used anymore.

When a mutex cannot be created, there must be something very wrong.
Induce panic and abort MPD in this case.

"struct notify" is the same as the "Notify" typedef.  It can be
forward-declared and has a lower case name.

git-svn-id: https://svn.musicpd.org/mpd/trunk@7367 09075e82-0dd4-0310-85a5-a0d7c8717e4f

This patch rewrites notify.c to use the pthread API, namely
pthread_mutex and pthread_cond.  This is a lot cheaper and easier than
the pipe() hack.

git-svn-id: https://svn.musicpd.org/mpd/trunk@7280 09075e82-0dd4-0310-85a5-a0d7c8717e4f