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

Replaces GLib's GError.

Cast to integer after multiplying with 1000.  Allows sub-second
seeking.

Pass a callback table to scan_file() and scan_stream(), instead of
returning a tag object.

When gme_track_info() returns with success, then the gme_info_t
pointer must be set.

this needs to be done for the end of songs to be detected.

Added macros with better names: GME_BUFFER_FRAMES, GME_BUFFER_SAMPLES
(the former only used to calculate the latter).

Move into enums.

Pass sizeof(buf) to decoder_data(), not the number of samples (which
is half the size).  At the same time, pass GME_BUF_SIZE to gme_play()
- libgme really wants to get the number of samples, not the number of
stereo frames.  Previously, this plugin had been using only the first
half of the buffer.

Allocate the "tag" object after the file has been opened successfully.

Supports a number of videogame music formats, more info here:
http://www.fly.net/~ant/libs/audio.html

I wrote this plugin for the latest svn, get it here:
http://code.google.com/p/game-music-emu/source/checkout