"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.

player_get_audio_format() replaces getPlayerSampleRate(),
getPlayerBits(), getPlayerChannels().

This replaces the attributes bits, channels, sampleRate.

Since the return value cannot be -1 anymore, we can make it unsigned.

The documentation for directory_update_init() was incorrect: a job ID
must be positive, not non-negative.  If the update queue is full and
no job was created, it makes more sense to return 0 instead of -1,
because it is more consistent with the return value of isUpdatingDB().

Remove clutter from directory.c.  Everything which saves or loads
to/from the hard disk goes to directory_save.c, and code which sends
directory information to the client is moved into directory_print.c.

With commit 6dcd7fea (if I am not mistaken) the error returned when
you try to save to an existing playlist is wrong.  Instead of
MPD_ACK_ERROR_EXIST, MPD_ACK_ERROR_NO_EXIST is returned.  This is
obviously wrong and breaks gmpc.

Yet another CamelCase removal patch.

The same can be achieved with directory_print(db_get_directory()).

Taming the directory.c monster, part II: move the database management
stuff to database.  directory.c should only contain code which works
on directory objects.

The source directory.c mixes several libraries: directory object
management, database management and database update, resulting in a
1000+ line monster.  Move the whole database update code to update.c.

This got broken when listHandlerFunc was removed.  Since we no
longer need it and it's confusing, remove processCommandInternal
and just use process_command.

commands should really not behave differently if they're issued
inside a command list or not; so stop having special handler
functions to deal with them.  "update" was the only command
that used this functionality and I changed that in the last
commit to serialize access.

Now the "update" command can be issued multiple times regardless
of whether the client is in list mode or not.

We serialize the update tasks to prevent updates from trampling
over each other and will spawn another update task
once the current one is finished updating and reaped.

Right now we cap the queue size to 32 which is probably enough (I
bet most people usually run update with no argument anyways);
but we can make it grow/shrink dynamically if needed.  There'll
still be a hard-coded limit to prevent DoS attacks, though.

Do full C99 integer type conversion in all modules which were not
touched by Eric's merged patch.

This only breaks "update" under list command mode and
no other commands.  This can be done more optimally
without the extra heap allocation via xstrdup(); but is
uncommon enough to not matter.

Due to a merge error, I broke the function handleUpdate().  It did not
do anything for the global update, and it did not send a proper
response to the client.  This patch fixes both bugs.

With patch 8d2830b3, I broke "addid": it did not return the id of the
new song, because of a typo in the return condition (== instead of
!=).

A lot of the preparation was needed (and done in previous
months) in making update thread-safe, but here it is.

This was the first thing I made work inside a thread when I
started mpd-uclinux many years ago, and also the last thing I've
done in mainline mpd to work inside a thread, go figure.

print_playlist_result() had an assert(0) at the end, in case there was
an invalid result value.  With NDEBUG, this resulted in a function not
returning a value - add a dummy "return -1" at the end to keep gcc
quiet.

Don't pass a pointer to client->permission to processCommand(), better
let the code in command.c use the new permission getter/setter
functions.

Some functions don't want to modify a client's permission set.  Pass
the permissions to them by value, not by reference.

Pass the client struct instead.

Pass the client struct instead of the raw file descriptor.

Pass the client struct instead of the raw file descriptor.

Pass the client struct instead of the raw file descriptor.

String literals (including those defined in CPP macros) can be
concatenated at compile time.  This saves some CPU cycles in
vsnprintf() at run time.

commandError() has been superseded by command_error(), and is not
being used anymore.  Remove it.

The function loadPlaylist() wants to report incremental errors to the
client, for this reason we cannot remove its protocol dependency right
now.  Instead, make it use the client struct instead of the raw file
descriptor.

Don't pass the raw file descriptor around.  This migration patch is
rather large, because all of the sources have inter dependencies - we
have to change all of them at the same time.

Pass the client struct to CommandHandlerFunction and
CommandListHandlerFunction.  Most commands cannot take real advantage
of that yet, since most of them still work with the raw file
descriptor.

Instead of passing the file descriptor, pass the client struct to
getCommandEntryAndCheckArgcAndPermission().

These two functions take a client struct instead of the file
descriptor.  We will now begin passing the client struct around
instead of a raw file descriptor (which needed a linear lookup in the
client list to be useful).

No protocol code in the audio output library.

The "volume" library shouldn't talk to the client.  Move error
handling to command.c.

Again, move error handling to command.c.

Move another ocurrence of error handling over to command.c.

This patch continues the work of the previous patch: don't pass a file
descriptor at all to traverseAllIn().  Since this fd was only used to
report "directory not found" errors, we can easily move that check to
the caller.  This is a great relief, since it removes the dependency
on a client connection from a lot of enumeration functions.

Continuing the effort of removing protocol specific calls from the
core libraries: let the command.c code call commandError() based on
PlaylistInfo's return value.

Return an "enum playlist_result" value instead of calling
commandError() in storedPlaylist.c.