Fixes a regression introduced in
560cb51e7b37e2c6f6fe4b72a3781185c57fdf83, which would lead this test on
x86_64-linux to return a DIFF with two packages, nhc98 and dev86 (both
have #:system "i686-linux" and thus depend on a different glibc object;
why other system-specific packages such as 'wine' aren't reported is
unclear).

* tests/graph.scm ("node-transitive-edges + node-back-edges"): Use
'test-equal'.  Define 'system-specific?' and use it.

* gnu/packages/bioinformatics.scm (deeptools): Remove variable.
* gnu/packages/efi.scm (efi_analyzer): Ditto.
* gnu/packages/guile.scm (guile-2.2/bug-fix, guile-json): Ditto.
* gnu/packages/image.scm (libjpeg): Ditto.
* gnu/packages/kde.scm (kdevplatform): Ditto
* gnu/packages/linphone.scm (linphoneqt): Ditto.
* gnu/packages/maths.scm (blis-sandybridge, blis-haswell, blis-knl): Ditto.
* gnu/packages/mpi.scm (hwloc-2.0): Ditto.
* gnu/packages/music.scm (python-abjad, zlfo): Ditto.
* gnu/packages/perl.scm (perl-base, perl-parent): Ditto.
* gnu/packages/tryton.scm (python-trytond): Ditto.
* gnu/packages/video.scm (gnome-mpv): Ditto.
* tests/graph.scm: Use guile-json-1.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

These modules would use (guix grafts) just to access '%graft?' and
related bindings, which are now in (guix store).

* gnu/ci.scm,
guix/gexp.scm,
guix/lint.scm,
guix/scripts.scm,
guix/scripts/archive.scm,
guix/scripts/build.scm,
guix/scripts/challenge.scm,
guix/scripts/deploy.scm,
guix/scripts/environment.scm,
guix/scripts/home.scm,
guix/scripts/pack.scm,
guix/scripts/package.scm,
guix/scripts/pull.scm,
guix/scripts/size.scm,
guix/scripts/system.scm,
guix/scripts/weather.scm,
tests/builders.scm,
tests/channels.scm,
tests/cpan.scm,
tests/derivations.scm,
tests/gexp.scm,
tests/graph.scm,
tests/guix-daemon.sh,
tests/monads.scm,
tests/pack.scm,
tests/packages.scm,
tests/profiles.scm,
tests/system.scm: Remove #:use-module (guix grafts).

* tests/graph.scm ("reverse bag DAG"): Adjust to latest OCaml changes by
looking at dune/ocaml-camomile/ocaml-utop.

* tests/graph.scm ("package DAG, oops it was a cycle"): New test.

* guix/graph.scm (export-graph): Add #:max-depth and honor it, adding
'depths' argument to 'loop'.
* guix/scripts/graph.scm (%options, show-help): Add '--max-depth'.
(%default-options): Add 'max-depth'.
(guix-graph): Pass #:max-depth to 'export-graph'.
* tests/graph.scm ("package DAG, limited depth"): New test.
* doc/guix.texi (Invoking guix graph): Document it.

This is a followup to 339177956affdc471832750a3805b74356487e93.

* tests/graph.scm ("reverse bag DAG"): Look for "ocaml4.07-dune" rather
than "dune".

* guix/packages.scm (<content-hash>): New record type.
(define-content-hash-constructor, build-content-hash)
(content-hash): New macros.
(print-content-hash): New procedure.
(<origin>): Rename constructor to '%origin'.
[sha256]: Remove field.
[hash]: New field.  Adjust users.
(origin-compatibility-helper, origin): New macros.
(origin-sha256): New deprecated procedure.
(origin->derivation): Adjust accordingly.
* tests/packages.scm ("package-source-derivation, origin, sha512"): New
test.
* guix/tests.scm: Hide (gcrypt hash) 'sha256' for proper syntax
matching.
* tests/challenge.scm: Add #:prefix for (gcrypt hash) and adjust users.
* tests/derivations.scm: Likewise.
* tests/store.scm: Likewise.
* tests/graph.scm ("bag DAG, including origins"): Provide 'sha256' field
with the right length.
* gnu/packages/aspell.scm (aspell-dictionary)
(aspell-dict-ca, aspell-dict-it): Use 'hash' and 'content-hash' for
proper syntax matching.
* gnu/packages/bash.scm (bash-patch): Rename 'sha256' to 'sha256-bv'.
* gnu/packages/bootstrap.scm (bootstrap-executable): Rename 'sha256' to 'bv'.
* gnu/packages/readline.scm (readline-patch): Likewise.
* gnu/packages/virtualization.scm (qemu-patch): Rename 'sha256' to
'sha256-bv'.
* guix/import/utils.scm: Hide (gcrypt hash) 'sha256'.

* guix/graph.scm (shortest-path): New procedure.
* tests/graph.scm ("shortest-path, packages + derivations")
("shortest-path, reverse packages")
("shortest-path, references"): New tests.

The graph traversal procedures in (guix graph) assume that nodes can be
compared with 'eq?', which was not the case for nodes of
%REFERENCE-NODE-TYPE and %REFERRER-NODE-TYPE (strings).

* guix/scripts/graph.scm (intern): New procedure.
(ensure-store-items, references*)
(%reference-node-type, non-derivation-referrers)
(%referrer-node-type): Use it on all store items.
* tests/graph.scm ("node-transitive-edges, references"): New test.