without a call to mpg123_scan the length returned by mpg123_length is not necessarly accurate (well, even in that case it's not guaranteed to be exact, i.e. if a file is modified while it's playing.) fixes the length reporting on some mp3 files i had around.

it didn't send the IMSG_CTL_COMMIT final message so it would get stuck. This also makes 'amused flush' redundant since it's possible to 'amused load </dev/null'.

like the one from bsd.port.mk, here it's used to decide the name of the tarball.