distro: Change the module name space to (gnu ...).

* distro: Rename to...
* gnu: ... this.  Update module names accordingly.
* Makefile.am: Adjust accordingly.
* po/POTFILES.in: Likewise.
* distro.scm: Search for files under /gnu/packages instead of
  /distro/packages.
* gnu/packages/base.scm (ld-wrapper-boot3): Likewise.

Merge branch 'core-updates'

Conflicts:
	guix/build/union.scm

Update license headers of builder-side code.

Change license headers with this script:

  (use-modules (guix build utils))

  (fluid-set! %default-port-encoding "UTF-8")

  (substitute* (cons "distro/packages/ld-wrapper.scm"
		     (find-files "guix/build" "\\.scm$"))
    (("^([[:graph:]]+) This file is part of Guix." _ comment-start)
     (string-append comment-start " This file is part of GNU Guix."))
    (("^([[:graph:]]+) Guix --- Nix package management.*" _ comment-start)
     (string-append comment-start
		    " GNU Guix --- Functional package management for GNU\n"))
    (("^([[:graph:]]+) Guix is " _ comment-start)
     (string-append comment-start " GNU Guix is "))
    (("^([[:graph:]]+) along with Guix." _ comment-start)
     (string-append comment-start " along with GNU Guix."))
    (("^([[:graph:]]+) Copyright \\(C\\)" _ comment-start)
     (string-append comment-start " Copyright ©")))

* distro/packages/ld-wrapper.scm, guix/build/download.scm,
  guix/build/gnu-build-system.scm, guix/build/union.scm,
  guix/build/utils.scm: Update license headers.

distro: ld-wrapper: Use the current Bash instead of /bin/sh.

* distro/packages/ld-wrapper.scm: Use @BASH@ in shebang.  Change module
  name to (gnu build-support ld-wrapper).
* distro/packages/base.scm (ld-wrapper-boot3): Substitute @BASH@.
  (ld-wrapper): Use BASH-FINAL.

distro: Rename (distro ...) to (distro packages ...).

* distro/base.scm, distro/ld-wrapper.scm: Move to `distro/packages'.
  Adjust LD-WRAPPER-BOOT3 input file name accordingly.
* Makefile.am (MODULES): Adjust accordingly.
* distro.scm (%distro-module-directory): Change to "/distro/packages".
* guix/build-system/gnu.scm (standard-inputs): Change module name
  to (distro packages base).
* tests/packages.scm (test-packages): Likewise.

distro: Add an `ld' wrapper, to pass missing `-rpath' flags.

* distro/ld-wrapper.scm: New file.
* Makefile.am (MODULES): Add it.

* distro/base.scm (ld-wrapper-boot3): New variable.
  (%boot3-inputs): Add LD-WRAPPER-BOOT3.
  (bash-final, guile-final, ld-wrapper): New final.
  (%final-inputs): Use BASH-FINAL; add LD-WRAPPER.
  (gcc-4.7): Remove the `-rpath' trick from the `lib' spec string.