Running `guix shell --pure ghc-esqueleto -D ghc-bytestring-builder`
results in an environment that has the base64-bytestring package (from
ghc-base64-bytestring) visible, even though it is not listed on listed
the command line (ghc-bytestring-builder doesn't dependend on it). It
seems to "leak" from the inputs of ghc-esqueleto which does depend on
ghc-base64-bytestring.

Is this a bug in guix or is it unavoidable for some reason?