beets: Add dependencies for "badfiles" plugin.
beets: Add dependencies for "badfiles" plugin.

I have to admit that I did very poor testing in d7307d8 and didn't
notice that the "badfiles" plugin relies on mp3val (thanks to @devhell
for packaging in 6e1ef13) and flac to be actually useful.

We now patch in the store locations of these binaries and make
"badfiles" an optional dependency (though enabled by default).

Now, I have tested "beet bad" on my whole music collection and it worked
fine (well, it has found errors... but that's what it is for).

Signed-off-by: aszlig <ee1aa092358634f9c53f01b5a783726c9e21b35a@redmoonstudios.org>

NixOS/nixpkgs,SymbiFlow/nixpkgs,triton/triton,SymbiFlow/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,triton/triton,SymbiFlow/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,triton/triton,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,triton/triton,NixOS/nixpkgs,triton/triton,SymbiFlow/nixpkgs,NixOS/nixpkgs,triton/triton,SymbiFlow/nixpkgs,triton/triton,NixOS/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,triton/triton