Sanitize filename sanitization and quoting. I'm not sure why i was

s/[:'"]/_/g, momentary insanity i suppose.  All i need do is replace /
with _ on output filenames and replace ' with '\'' on filenames that
will go to the shell surrouned by '' quotes, instead of being passed
directly into a program's argv.

fa-flacd:
    (flac): Do / sanitization only, since we're not going through the
    shell, but running flac directly.

flac2mp3:
    (flac2mp3): We weren't sanitizing the input filename; start doing
    so.  Only do ' sanitization for input file and output id3tag
    information, additionally do / sanitization on $outfile.