union: Detect collisions, and delete duplicate leaves.

* guix/build/union.scm (delete-duplicate-leaves): New procedure.
  (union-build)[leaf=?, resolve-collision]: New procedures.
  Use `delete-duplicate-leaves' on the result of `tree-union'.
* tests/union.scm ("delete-duplicate-leaves, default",
  "delete-duplicate-leaves, file names"): New tests.

guix-package: Create ~/.guix-profile when it doesn't exist.

* guix-package.in (guix-package): Create the %USER-ENVIRONMENT-DIRECTORY
  symlink if it doesn't exist yet.
* doc/guix.texi (Invoking guix-package): Document it.

guix-package: Show package outputs in `--list-available'.

* guix-package.in (guix-package)[process-query]: For `list-available',
  show the outputs of each package.
* doc/guix.texi (Invoking guix-package): Update accordingly.

doc: Update copyright years; add visible copyright statement.

* doc/guix.texi (YEARS): New variable.
  Use it for all copyright statements.
  (Top): Add a copyright statement and license header here.

doc: Documentation installation and the daemon.

* doc/guix.texi (Installation): New node.

daemon: Fix warning message when running as root without a build user group.

* nix/nix-daemon/guix-daemon.cc (main): Fix warning message when running
  as root without `--build-users-group'.

guix-daemon: Rename `--build-cores' for consistency with `guix-build'.

* nix/nix-daemon/guix-daemon.cc (options): Change `--build-cores' to
  `--cores', and `-C' to `-c'.
  (parse_opt): Adjust accordingly.

derivations: Fix `derivation-prerequisites-to-build' when outputs are there.

Before it would list inputs not built, even if the outputs of the given
derivation were already available.

* guix/derivations.scm (derivation-prerequisites-to-build): Add
  `outputs' keyword parameter.
  [built?, derivation-built?]: New procedures.
  [loop]: Add `sub-drvs' parameter.  Use `derivation-built?' to check if
  the SUB-DRVS of DRV are built before checking its inputs.

gnu-maintenance: Add `latest-release' and related tools.

* guix/gnu-maintenance.scm (ftp-server/directory, releases,
  version-string>?, latest-release, gnu-package-name->name+version): New
  procedures.
  (%package-name-rx): New variable.

guix-package: Use `guile-final', not `guile-2.0' to build the environment.

* guix-package.in (guix-package): Use either %BOOTSTRAP-GUILE or
  GUILE-FINAL.

guix-package: Be verbose when Guile itself needs to be built.

* guix-package.in (guix-package)[guile-missing?]: New procedure.
  (guix-package): Always redirect `current-build-output-port' to
  `current-error-port' when (guile-missing?).

guix-package: Remove `-b' shorthand for `--bootstrap'.

* guix-package.in (%options): Remove #\b as an alternate for
  "bootstrap".
  (show-help): Adjust accordingly.
* tests/guix-package.sh: Use `--bootstrap' instead of `-b'.

snix: Update `license' check in unit test.

* tests/snix.scm ("nixpkgs->guix-package"): Expect `license' to be a
  symbol.  This is a follow-up to commit e7aa73e.

snix: Use (guix licenses) variables.

* guix/snix.scm (snix-derivation->guix-package)[license-variable]: New
  procedure.
  Use it to determine the variable name for the license.

snix: Gracefully handle `null' in Nix build inputs.

* guix/snix.scm (snix-derivation->guix-package)[convert-inputs]:
  Gracefully handle `null' as an input.

distro: Add GNU Aspell.

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

distro: Add GSL.

* distro/packages/algebra.scm (gsl): New variable.

distro: Add GNU GLOBAL.

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

distro: Add Tcl, Expect, and DejaGNU.

* distro/packages/dejagnu.scm, distro/packages/tcl.scm: New files.
* Makefile.am (MODULES): Add them.

Update license headers.

Change all license headers, except guix/build/* and ld-wrapper.scm, with
this code:

  (use-modules (guix build utils)
	       (srfi srfi-1))

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

  (substitute* (remove (lambda (f)
			 (or (string-contains f ".tar.")
			     (string-contains f ".git/")
			     (string-contains f ".so")
			     (string-suffix? ".o" f)
			     (string-suffix? ".a" f)
			     (string-suffix? ".go" f)
			     (string-suffix? ".pdf" f)
			     (string-suffix? ".png" f)
			     (string-suffix? ".info" f)
			     (equal? (basename f) "guix-daemon")
			     (equal? (basename f) "nix-setuid-helper")
			     (string-contains f "nix-upstream/")
			     (string-contains f "distro/packages/bootstrap/")))
		       (find-files "." "\\.[a-z]+$"))
    (("^([[: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 ©")))

Change headers using C-style comments manually.