/*
* Get the file path of a song.
*
* This method raises an Xmms::Error exception if XMMS is not running,
* or an ArgumentError exception if the number of arguments isn't 0 or
* 1.
*
* Examples:
* # get the path of the current song
* path = remote.file
*
* # get the path of song 23 in the playlist
* path = remote.file 23
*
*/
static VALUE xr_pl_file(int argc, VALUE *argv, VALUE self) {