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.

distro: gcc: Don't add a RUNPATH to GCC when using `-static-libgcc'.

* distro/packages/base.scm (gcc-4.7)[LIB_SPEC]: Add a `-rpath' to GCC
  only when !static and !static-libgcc.

distro: readline: Allow stripping of the libraires.

* distro/packages/readline.scm (readline)[arguments]: Add `post-install'
  phase to make libraries writable.

utils: Add `default-keyword-arguments' and `substitute-keyword-arguments'.

* distro/packages/base.scm (default-keyword-arguments,
  substitute-keyword-arguments): Move to...
* guix/utils.scm: ... here.

distro: Add missing `package-with-bootstrap-guile'.

* distro/packages/base.scm (binutils-final): Add missing
  `package-with-bootstrap-guile'.

distro: recutils: Comment out optional dependencies.

* distro/packages/recutils.scm (recutils): Comment out optional
  dependencies not packaged here.

distro: Add GnuPG and companion libraries.

* distro/packages/gnupg.scm: New file.
* Makefile.am (MODULES): Add it.