Search'n'replace typo..

directory_update_init() has to be called with a path that is already
sanitized.  Don't call sanitizePathDup() again in updatePath().

The algorithm in addDirectoryPathToDB() can be simplified further if
it is combined with the function addParentPathToDB().  Since there is
no other caller of addDirectoryPathToDB(), we can do that.  This saves
another large stack buffer.

This recursive function is very dangerous because it allocates a large
buffer on the stack in every iteration.  That may be misused to
generate a stack overflow.

When a directory cannot be updated, there must be something wrong with
it, and the database contains stale data.  Remove it.

The branching looks a bit complicated in addDirectoryPathToDB() -
improve its readability by moving code to a simplified separate
function.

When the root directory fails to update, its contents are invalid.
Clear it then.

When a directory failed to update, it was removed from the database,
without freeing all children and songs (memory leak), and without
locking (race condition).  Introduce the functions clear_directory()
and delete_directory(), which do both.

Use updateInDirectory() instead of addToDirectory().  Eliminate a
duplicate stat() in updateInDirectory() by calling song_file_update()
directly.

Don't use db_get_directory() and traverse the full path with every
directory being loaded.  Just see if the current parent contains the
entry.  Everything else would be invalid anyway..

A manipulated database could trigger an assertion failure, because the
parent didn't match.  Do a proper check if the new directory is within
the parent's.  This uses FATAL() to bail out, so MPD still dies, but
it doesn't crash.

Some tiny utilities... wrappers like these may become helpful when we
introduce locking.

dirvec_find() does not modify the object, thus it should get a const
pointer.

No idea why it was created in directory.h, but it should be in
dirvec.h.

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.

Use sizeof(buffer) instead.

Removed a superfluous closure.

Having an array with disabled entries sucks.  Removed that
DISABLED_SHOUT_ENCODER_PLUGIN macro, and fill the plugin list only
with plugins which are actually enabled.  This should be done for all
plugin types.

In the libsamplerate fallback code, a "const" attribute was missing.

"volume" was passed as an unsigned integer, which is correct.  It's
just that when it was multiplied with the sample value, the whole
operation was changed to unsigned, breaking the algorithm (and Qball's
ears).  Internally change "volume" to signed.

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.

Commit 0bfe7802 broke update for new files in the root directory,
because music_root->path was an empty string and not NULL.  There were
some NULL tests missing.  Change them to !isRootDirectory(path)
instead of path!=NULL.

Due to a merge error, reap_update_task() called cond_signal_async()
with a locked mutex.  That always fails.  Use cond_signal_sync()
instead.

ino_t and dev_t are declared in sys/types.h, not sys/stat.h.

For the root directory, let's set path to an empty string.  This saves
a few checks.

Also convert directory_get_path() to an inline function, which returns
a constant string.

CamelCase is ugly, rename the functions.

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 function isRootDirectory() is tiny and can be converted to an
inline function.  Don't allow name==NULL.

The runtime check suggests that the author has somehow thought
song_get_url(NULL) might be valid.  It should not be.  Replace it with
an assertion.

Eliminate duplicated code.

Instead of returning 0 or -1, return true on success and false on
failure.  This seems more natural, and when the C library was
designed, there was no "bool" data type.

This function was never used on remote songs.  Replace the runtime
check with an assertion.

CamelCase is ugly...  rename all functions.

Provide separate constructors for creating a remote song, a local
song, and one for loading data from a song file.  This way, we can add
more assertions.

Check the old status before assigning.  This saves a temporary
variable.

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