Merge branch 'master' into core-updates

hydra: Pass the directory name of the Nix checkout.

* build-aux/hydra/guix.scm (hydra-jobs): Extract the 'file-name' item
  from NIX-CHECKOUT, and pass that to 'tarball-package'.

hydra: Fix typo.

* build-aux/hydra/guix.scm (tarball-package): Unquote 'nix-checkout'.

hydra: Add missing import.

* build-aux/hydra/gnu-system.scm, build-aux/hydra/guix.scm: Use (guix
  derivations).

hydra: Return the .drv file names, not the <derivation> objects.

* build-aux/hydra/gnu-system.scm (package->alist): Call
  'derivation-file-name' on the result of 'package-derivation'.
* build-aux/hydra/guix.scm (package->alist): Likewise.

hydra: Point the Git submodule to our local copy.

* build-aux/hydra/guix.scm (tarball-package): Add 'nix-checkout'
  parameter.  Replace 'patch-bootstrap-script' phase by
  'set-nix-module'.
  (hydra-jobs): Get the 'nix' value from ARGUMENTS, and pass it to
  'tarball-package'.

Merge branch 'master' into core-updates

hydra: Add Graphviz as an input to the "tarball" job.

* build-aux/hydra/guix.scm (tarball-package): Add GRAPHVIZ to
  `native-inputs'.

hydra: Add Git as an input to the "tarball" job.

* build-aux/hydra/guix.scm (tarball-package): Add `native-inputs' field.

hydra: Comment out all Git invocations in `bootstrap'.

* build-aux/hydra/guix.scm (tarball-package): Comment out all `git'
  invocations.

hydra: Add missing import.

* build-aux/hydra/guix.scm: Use (srfi srfi-26).

hydra: Add missing import.

* build-aux/hydra/guix.scm: Use (srfi srfi-26).

hydra: Return a symbol/thunk pair.

* build-aux/hydra/guix.scm (hydra-jobs): Return a symbol/thunk pair.

hydra: Extract the actual file name from the Guix checkout.

* build-aux/hydra/guix.scm (hydra-jobs): Extract the `file-name' part of
  CHECKOUT.

hydra: Add job to run "make distcheck" on Guix.

* build-aux/hydra/guix.scm: New file.
* Makefile.am (EXTRA_DIST): Add it.