Add `guix-gc'.

* guix-gc.in, tests/guix-gc.sh: New files.
* configure.ac: Output `guix-gc', and make it executable.
* Makefile.am (bin_SCRIPTS): Add `guix-gc'.
  (TESTS): Add `tests/guix-gc.sh'.
* doc/guix.texi (Features): Add xref to "Invoking guix-gc".
  (Invoking guix-gc): New node.
* po/POTFILES.in: Add `guix-gc.in'.

tests/guix-gc.sh

@@ -0,0 +1,54 @@
+# Guix --- Nix package management from Guile.         -*- coding: utf-8 -*-
+# Copyright (C) 2013 Ludovic Courtès <ludo@gnu.org>
+#
+# This file is part of Guix.
+#
+# Guix is free software; you can redistribute it and/or modify it
+# under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or (at
+# your option) any later version.
+#
+# Guix is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+#
+# Test the `guix-gc' command-line utility.
+#
+
+guix-gc --version
+
+trap "rm -f guix-gc-root" EXIT
+rm -f guix-gc-root
+
+# Add then reclaim a .drv file.
+drv="`guix-build idutils -d`"
+test -f "$drv"
+
+guix-gc --list-dead | grep "$drv"
+guix-gc --delete "$drv"
+! test -f "$drv"
+
+# Add a .drv, register it as a root.
+drv="`guix-build --root=guix-gc-root lsh -d`"
+test -f "$drv" && test -L guix-gc-root
+
+guix-gc --list-live | grep "$drv"
+if guix-gc --delete "$drv";
+then false; else true; fi
+
+rm guix-gc-root
+guix-gc --list-dead | grep "$drv"
+guix-gc --delete "$drv"
+! test -f "$drv"
+
+# Try a random collection.
+guix-gc -C 1KiB
+
+# Check trivial error cases.
+if guix-gc --delete /dev/null;
+then false; else true; fi