Refactor SimpleDatabase::GetLastModified() to be generic for all
plugins.  Remove the SimpleDatabase assumption from db_stats_print(),
allowing it to be implemented by all database plugins.

Fixes crash on "stats" in certain configurations.

Eliminate redundant declaration.

Unused outside of Stats.cxx.

Publish the Client API, preparing to move more code into the Client
class.

Use forward declaration instead.

Prepare to migrate away from GLib.  Currently, we're still using GLib
as a backend.

Replaces GLib's GError.

Optimize the ProxyDatabase by invoking "stats" on the peer, instead of
visiting all songs.

Preparing for non-"simple" database plugins.

Fixes warning on mingw32.

Add nonnull attributes and fix all callers.

Use this struct for db_walk().

Allocate a player_control object where needed, and pass it around.
Each "client" object is associated with a "player_control" instance.

This prepares multi-player support.

After we've been hit by Large File Support problems several times in
the past week (which only occur on 32 bit platforms, which I don't
have), this is yet another attempt to fix the issue.

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.

Renamed numOfItems to num_items.

time(NULL) shows the wrong results when the machine's clock is
changed.

Don't use dbUtils.h functions.  This reduces 4 full database walks to
just one.

Don't recalculate the number of artists and albums each time a client
requests statistics.  Calculate that once in stats_update().

Renamed functions and types.