nix why-depends: Add option to show all edges causing a dependency
nix why-depends: Add option to show all edges causing a dependency

For example, without --all:

  $ nix why-depends nixpkgs.nixUnstable nixpkgs.libssh2
  /nix/store/s9n5gvj2l49b4n19nz6xl832654nf7n7-nix-1.12pre5511_c94f3d55
  └───lib/libnixstore.so: …/lib:/nix/store/w9ykqpl5v0r3vfwsgn408jqhs72cx96x-curl-7.55.0/lib…
      => /nix/store/w9ykqpl5v0r3vfwsgn408jqhs72cx96x-curl-7.55.0
      └───lib/libcurl.la: …ib -L/nix/store/4mbayl1y5hpjbjzkx8ndyhkv98kqw1wi-libssh2-1.8.0/l…
          => /nix/store/4mbayl1y5hpjbjzkx8ndyhkv98kqw1wi-libssh2-1.8.0

but with --all:

  $ nix why-depends -a nixpkgs.nixUnstable nixpkgs.libssh2
  /nix/store/s9n5gvj2l49b4n19nz6xl832654nf7n7-nix-1.12pre5511_c94f3d55
  ├───lib/libnixstore.so: …/lib:/nix/store/w9ykqpl5v0r3vfwsgn408jqhs72cx96x-curl-7.55.0/lib…
  │   => /nix/store/w9ykqpl5v0r3vfwsgn408jqhs72cx96x-curl-7.55.0
  │   └───lib/libcurl.la: …ib -L/nix/store/4mbayl1y5hpjbjzkx8ndyhkv98kqw1wi-libssh2-1.8.0/l…
  │       lib/libcurl.so.4.4.0: …/lib:/nix/store/4mbayl1y5hpjbjzkx8ndyhkv98kqw1wi-libssh2-1.8.0/l…
  │       => /nix/store/4mbayl1y5hpjbjzkx8ndyhkv98kqw1wi-libssh2-1.8.0
  └───lib/libnixstore.so: …/lib:/nix/store/bx2i9vi76lps6w9rr73fxf6my31s4dg5-aws-sdk-cpp-1.0…
      => /nix/store/bx2i9vi76lps6w9rr73fxf6my31s4dg5-aws-sdk-cpp-1.0.153
      └───lib/libaws-cpp-sdk-core.so: …e.so./nix/store/w9ykqpl5v0r3vfwsgn408jqhs72cx96x-curl-7.55.0/lib…
          lib/libaws-cpp-sdk-s3.so: …/lib:/nix/store/w9ykqpl5v0r3vfwsgn408jqhs72cx96x-curl-7.55.0/lib…
          => /nix/store/w9ykqpl5v0r3vfwsgn408jqhs72cx96x-curl-7.55.0

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