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 'master' into nix-integration

distro: Add GNU lsh.

* distro/packages/lsh.scm,
  distro/packages/patches/lsh-guile-compat.patch:
  distro/packages/patches/lsh-no-root-login.patch:
  distro/packages/patches/lsh-pam-service-name.patch: New files.
* Makefile.am (MODULES): Add lsh.scm.
  (dist_patch_DATA): Add the above patches.