* gnu/system/install.scm (self-contained-tarball): Move to...
* guix/scripts/pack.scm: ... here.  New file.
* doc/guix.texi (Binary Installation): Mention 'guix pack'.
(Invoking guix pack): New node.
* build-aux/make-binary-tarball.scm: Remove.
* Makefile.am (MODULES): Add guix/scripts/pack.scm.
(EXTRA_DIST): Remove build-aux/make-binary-tarball.scm.
(guix-binary.%.tar.xz): Rewrite using 'guix pack'.
* build-aux/hydra/gnu-system.scm (tarball-jobs): Adjust accordingly.