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

distro: make-bootstrap: Have libc's functions search for `sh' in $PATH.

* distro/packages/make-bootstrap.scm (%glibc-with-relocatable-system,
  %standard-inputs-with-relocatable-glibc): New variables.
  (%static-inputs)[gawk]: Apply `gawk-shell.patch'.
  [finalize]: New procedure.
  Build all the packages against %STANDARD-INPUTS-WITH-RELOCATABLE-GLIBC.
  (%glibc-stripped): Inherit from %GLIBC-WITH-RELOCATABLE-SYSTEM.
  (%gcc-static, %guile-static): Build against
  %STANDARD-INPUTS-WITH-RELOCATABLE-GLIBC.
* distro/packages/patches/gawk-shell.patch,
  distro/packages/patches/glibc-bootstrap-system.patch: New files.
* Makefile.am (dist_patch_DATA): Add them.