WIN32 does have some kind of symbolic links (e.g. in NTFS), but the
readlink() function is not available.  Disable symlink checking for
now.

WIN32 doesn't have POSIX signals.  Disable the code.  For a complete
port, we will have to implement the WIN32 equivalent.

Due to a typo, adding local files was always denied.

Disable the second playlist_append_file() invocation on WIN32.

It's been superseded by GLib's GSList.

Use GLib's singly-linked list library instead of our custom one.

JACK documentation states: "The caller is responsible for calling
free(3) any non-NULL returned value."

This does not seem to include the array elements.  Duplicate them
after jack_get_ports(), and free only the array.  Convert
JackData.output_ports to non-const.

There is only one location using PIPE_EVENT_SIGNAL: to synchronize
player_command() with player_command_finished().  Use the "notify"
library instead of the event_pipe here.

Don't use fixed stack buffers.

Don't use fixed stack buffers.

If we want to check whether a file is a directory, use GLib's
g_file_test() instead of stat().

Use G_GNUC_UNUSED instead of mpd_unused (which has already been
removed).

To find out whether a file exists, use g_file_test() instead of
stat(), because it is more portable and easier to use.

Don't pass a static buffer to map_spl_utf8_to_fs().

If no music_directory is configured, fall back to the XDG music
directory, determined by
g_get_user_special_dir(G_USER_DIRECTORY_MUSIC).

Nobody is using the signal_check library anymore.

This patch also removes the SIGUSR1 handler.

The signal_check library went out of order when we started using the
GLib main loop.  Convert the SIGHUP handler to use event_pipe instead.

event_pipe_emit_fast() is aimed for use in signal handlers: it doesn't
lock the mutex, and doesn't log on error.  That makes it potentially
lossy, but for its intended use, that does not matter.

There is no reason to use the shortcut "mix" instead of "mixer".

Don't start the daemon when MPD is called with "--version".

Make the event_pipe (formerly main_notify) send/receive a set of
events, with a callback for each one.

The default event PIPE_EVENT_SIGNAL does not have a callback.  It
is still there for waking up the main thread, when it is waiting for
the player thread.

Continuing the previous patch.

We are going to migrate away from the concept of notifying the main
thread.  There should be events sent to it instead.  This patch starts
a series to implement that.

Removed all macros which are already provided by GLib.

Use GLib's G_GNUC_UNUSED instead of gcc.h's mpd_unused.

Use GLib's G_GNUC_UNUSED instead of gcc.h's mpd_unused.

Use GLib's G_GNUC_UNUSED instead of macros from gcc.h.

With the GLib main loop, the client manager can install its own event
in case a client is expired.  No need for main.c to call
client_manager_expire() manually.