This is the beginning of multi-player support.  There will be support
for multiple Partition objects in one MPD process.

Push the new mode to the filter instead of accessing global variables
through replay_gain_get_real_mode().

Move the configuration lookup to Main.cxx.

Don't free the string right after calling log_init_file().  Add a new
function log_deinit() that frees the string on shutdown.

This fixes cycling the log file after SIGHUP (Mantis ticket 0003524).

MPD requires GLib 2.16.

Eliminates explicit global initialisation.

The new block overrides the "db_file" setting, and allows configuring
any database plugin.

Let the caller take care for legacy conversion.

Useless call.

After a previous refactor, the current code fails on paths that need
expansion (e.g, '~/.mpd/sticker.db'), because we are not passing the correct
path to the sticker database code. Pass the expanded (and previously unused)
string instead of the original string.
Signed-off-by: Dan McGee <dan@archlinux.org>

size_t is unsigned most of the time, so we can't really use it to
check for negative values. Also handle strtol overflow.

Load the samplerate_converter on MPD startup.  Fail if the converter
name is invalid.

First draft, not really pluggable currently - hard-coded to use the
"simple" plugin, and calls several of its internal functions.

The API is very simple currently, all searches are still performed
over the root "directory" object.  Future changes to the API will move
those search implementations into the plugin, to allow more efficient
implementations, or implementations that don't have the whole tree in
memory all the time.

config_get_path() was somewhat flawed, because it pretended to be a
function, when it really had a side effect.  The second flaw was that
it did not return the parser error, instead it aborted the whole
process, which is bad style.  The new function returns a duplicated
(modified) string that must be freed by the caller, and returns a
GError on failure.