mp3_afh: Switch to UTF-8 encoding.

mp3_afh: Switch to UTF-8 encoding.

The interface of libid3tag allows to get the tag contents in various
formats. Currently, we always call the latin1 variants of these
library functions.

However, as UTF-8 encoding is more widespread these days and almost
all distributions, including the two year old Ubuntu lucid, have
switched to UTF-8, UTF-8 is probably a better choice today.

This patch changes mp3_afh.c to use the UTF-8 variants instead.