update headless_pianobar; $0 refers to func name when inside a func

$0 is the name of the script and $1,$2,..$x are command line args, unless you are inside a function.  Inside a function, $0 is the name of the function and $1,$2,..$x are args passed to the function.  So referencing $0 from w/in a function will give you the name of the function, not the name of the script as desired.  Easy fix tho.