gnu: hello: Upgrade to 2.9.

* gnu/packages/base.scm (hello): Upgrade to 2.9.  Remove 'arguments' and
  'inputs' fields, which were never needed.

gnu: libextractor: Upgrade to 1.2.

* gnu/packages/gnunet.scm (libextractor): Upgrade to 1.2.

gnu: freeipmi: Upgrade to 1.3.3.

* gnu/packages/freeipmi.scm (freeipmi): Upgrade to 1.3.3.

gnu: rcs: Upgrade to 5.9.1.

* gnu/packages/version-control.scm (rcs): Upgrade to 5.9.1.  Add ed as
  an input.

gnu: lightning: Upgrade to 2.0.2.

* gnu/packages/lightning.scm (lightning): Upgrade to 2.0.2.

gnu: linux-libre: Upgrade to 3.12.

* gnu/packages/linux.scm (linux-libre): Upgrade to 3.12.

gnu: vm: Really create a QCOW2-format image.

* gnu/system/vm.scm (expression->derivation-in-linux-vm): Pass "-f
  qcow2" to 'qemu-img create'.

doc: Link to package-list.html.

* doc/guix.texi (GNU Distribution): Add link to package-list.html.

list-packages: Produce link to the origin snippet, if any.

* build-aux/list-packages.scm (package->sxml)[patches](snippet-link):
  New procedure.
  Use it to produce a link to the 'origin-snippet', if any.

packages: 'package-field-location' returns a relative file name.

* guix/packages.scm (package-field-location): Set
  %FILE-PORT-NAME-CANONICALIZATION.
* tests/packages.scm ("package-field-location, relative file name"): New
  test.

guix build: '-e' can be passed a monadic thunk.

* guix/ui.scm (read/eval): New procedure.
  (read/eval-package-expression): Use it.
* guix/scripts/build.scm (derivations-from-package-expressions): Rename to...
  (derivation-from-expression): ... this.  Accept procedures, under the
  assumption that they are monadic thunk.
  (show-help): Adjust accordingly.
  (guix-build): Ditto.
* tests/guix-build.sh: Add test.
* doc/guix.texi (Invoking guix build): Augment description of '-e'.

doc: Mention Linux containers; emphasize reproducible builds.

* doc/guix.texi (Introduction): Use "containers" instead of "chroots".
  (Invoking guix-daemon): Add @cindex entries.  Mention the Linux
  container features.
  (Features): Add sentence on build reproducibility.

doc: Improve "Installing Guix from Guix" section.

Reported by Mark H. Weaver <mhw@netris.org>.

* README (Installing Guix from Guix): Explicitly mention $PATH
  separately.  Mention $ACLOCAL_PATH, not $ACLOCAL.  Give the exact
  command to install the dependencies.  Remove mention of
  $GUIX_LD_WRAPPER_ALLOW_IMPURITIES, which is no longer needed.

gnu: cflow: Install Emacs mode.

* gnu/packages/cflow.scm (cflow): Add Emacs as an input.

substitute-binary: Adjust timeout handling for Guile > 2.0.9.

* guix/scripts/substitute-binary.scm (with-timeout): Update comment to
  mention the fix's commit ID.
  (fetch): In the 'with-timeout' handler, close PORT only one Guile
  versions < 2.0.9.39.  Before that, on Guile >= 2.0.9.39, the HTTP
  client would end up trying to read from a closed file descriptor.

derivations: Allow 'map-derivations' to replace sources.

* guix/derivations.scm (map-derivation)[input->output-paths]: Allow
  non-derivation inputs.
  Allow replacements to be store files.  Replace in SOURCES too.
* tests/derivations.scm ("map-derivation, sources"): New test.

packages: Suitably cope with indirect store paths as package sources.

* guix/packages.scm (package-source-derivation): Don't let indirect
  store paths pass through.
* tests/packages.scm ("package-source-derivation, indirect store path"):
  New test.

store: Make 'direct-store-path?' public.

* guix/store.scm (direct-store-path?): New procedure.
* guix/derivations.scm (derivation)[direct-store-path?]: Remove.
* tests/store.scm ("direct-store-path?"): New test.

derivations: Add 'map-derivation'.

* guix/derivations.scm (map-derivation): New procedure.
* tests/derivations.scm ("map-derivation"): New test.

utils: Add 'string-replace-substring'.

* guix/utils.scm (string-replace-substring): New procedure.  Based on
  code by Mark H. Weaver.
* tests/utils.scm ("string-replace-substring"): New test.