Add (guix download) and (guix build download).

* guix/download.scm, guix/build/download.scm: New files.
* Makefile.am (MODULES): Add them.
* tests/builders.scm ("url-fetch"): New test.
* distro/packages/bootstrap.scm (bootstrap-origin): Support
  `url-fetch'.
* guix/snix.scm (snix-derivation->guix-package): Use `url-fetch' instead
  of `http-fetch'.

Move base32 code to (guix base32).

* guix/utils.scm (bytevector-quintet-ref, bytevector-quintet-ref-right,
  bytevector-quintet-length, bytevector-quintet-fold,
  bytevector-quintet-fold-right, make-bytevector->base32-string,
  %nix-base32-chars, %rfc4648-base32-chars, bytevector->base32-string,
  bytevector->nix-base32-string, bytevector-quintet-set!,
  bytevector-quintet-set-right!, base32-string-unfold,
  base32-string-unfold-right, make-base32-string->bytevector,
  base32-string->bytevector, nix-base32-string->bytevector): Move to...
* guix/base32.scm: ... here.  New file.

* tests/utils.scm (%nix-hash, "bytevector->base32-string",
  "base32-string->bytevector", "nix-base32-string->bytevector", "sha256
  & bytevector->base32-string"): Move to...
* tests/base32.scm: ... here.  New file

* guix-download.in, guix/derivations.scm, guix/packages.scm,
  guix/snix.scm, tests/builders.scm, tests/derivations.scm: Adjust
  accordingly.
* guix.scm (%public-modules): Add `base32'.

tests: Choose a less expensive test for packages.

* tests/packages.scm (%bootstrap-inputs): Remove.
  ("GNU Hello"): Rename to...
  ("GNU Make, bootstrap"): ... this.  Build GNU-MAKE-BOOT0 instead of
  HELLO.

http: Add informative output.

* guix/build/http.scm (http-fetch): Emit message indicating the
  download.

http: Check the HTTP response code, and bail if not 200.

* guix/build/http.scm (http-fetch): Check RESP's code; error out when
  it's not 200.

derivations: build-expression->derivation: Builder only refers to sources.

* guix/derivations.scm (build-expression->derivation)[source-path]: New
  procedure.
  [builder]: Pass only sources as references.  This fixes a bug whereby
  changing a fixed-output drv referred to by a builder would cause the
  builder's hash to change, thereby leading to a full rebuild.
* tests/derivations.scm ("build-expression->derivation with a
  fixed-output input"): New test.

derivations: Add tests relative to fixed-output derivations.

* tests/derivations.scm ("fixed-output derivation"): Add comment that
  the reference to BUILDER is optional.
  ("fixed-output derivation: output paths are equal",
  "derivation with a fixed-output input",
  "build-expression->derivation: same fixed-output path"): New tests.

store: Document `add-to-store' hack for `fixed?'.

* guix/store.scm (add-to-store): Document that `fixed?' must be #t.

guix-download: Print the hash of the file's contents, no that of the path.

* guix-download.in (guix-download): Display the hash of the contents of
  PATH, not the path hash.  Also, call `add-to-store' with FIXED? = #t.

guix-download: Error out when the HTTP response code is not 200.

* guix-download.in (http-fetch): Leave with an error message when
  RESPONSE's code is not 200.

* tests/guix-download.sh: New file.
* Makefile.am (TESTS): Add it.

guix-build: Error out when `-S' used for source-less package.

* guix-build.in (derivations-from-package-expressions): Leave with an
  error message when SOURCE? is #t and P has no source.

* tests/guix-build.sh: Add test.

doc: Document the features and `guix-package'.

* doc/guix.texi: Change the category to "Package management".  Add an
  @direntry for "Invoking guix-package".
  (Package Management): New chapter.

guix-package: Fix handling of the PACKAGE:OUTPUT syntax.

* guix-package.in (guix-package)[find-package]: Return the correct NAME
  and SUB-DRV when NAME contains #\:.

* tests/guix-package.sh (profile): Add test.

guix-package: Fix invalid module use.

* guix-package.in: Use (distro packages guile), not (... base).

build: Remove now unnecessary dependency of downloads on guix/utils.go.

* Makefile.am (distro/packages/bootstrap/x86_64-linux/guile-bootstrap-2.0.6.tar.xz,
  distro/packages/bootstrap/i686-linux/guile-bootstrap-2.0.6.tar.xz):
  Remove dependency on guix/utils.go.

doc: Document `guix-build'.

* doc/guix.texi (Invoking guix-build): Populate.

doc: Remove unnecessary @ifinfo.

* doc/guix.texi: Remove @ifinfo around @dir{category,entry}.  Suggested
  by Karl Berry <karl@freefriends.org>.

distro: Move bootstrap tarball packages to (distro packages make-bootstrap).

* distro/packages/base.scm (binutils-final): Make public.
  (static-package, %bash-static, %static-inputs, %static-binaries,
  %binutils-static, %binutils-static-stripped, %glibc-stripped,
  %gcc-static, %gcc-stripped, %guile-static, %guile-static-stripped,
  tarball-package, %bootstrap-binaries-tarball,
  %binutils-bootstrap-tarball, %glibc-bootstrap-tarball,
  %guile-bootstrap-tarball): Move to...
* distro/packages/make-bootstrap.scm: ... here.  New file.
* Makefile.am (MODULES): Add it.

distro: bash-final: Link with `-static-libgcc'.

* distro/packages/base.scm (bash-final): Pass through
  `static-libgcc-package'.

build-system/gnu: Add `static-libgcc-package' & supporting procedure.

* guix/build-system/gnu.scm (package-with-extra-configure-variable,
  static-libgcc-package): New procedures.