guix {system,offload}: Improve reporting of syntax errors.

* guix/scripts/system.scm (read-operating-system) <catch handler>: Add
  case for 'syntax-error'.  Correct message for default case.
* guix/scripts/offload.scm (build-machines) <catch handler>: Add case
  for 'syntax-error'.
* tests/guix-system.sh: New file.
* Makefile.am (SH_TESTS): Add it.

tests/guix-system.sh

@@ -0,0 +1,43 @@
+# GNU Guix --- Functional package management for GNU
+# Copyright © 2014 Ludovic Courtès <ludo@gnu.org>
+#
+# This file is part of GNU Guix.
+#
+# GNU 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.
+#
+# GNU 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 GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+#
+# Test the daemon and its interaction with 'guix substitute-binary'.
+#
+
+set -e
+
+guix system --version
+
+tmpfile="t-guix-system-$$"
+errorfile="t-guix-system-error-$$"
+trap 'rm -f "$tmpfile" "$errorfile"' EXIT
+
+cat > "$tmpfile"<<EOF
+;; This is line 1, and the next one is line 2.
+   (operating-system)
+;; The 'T' is at column 3.
+EOF
+
+if guix system vm "$tmpfile" 2> "$errorfile"
+then
+    # This must not succeed.
+    exit 1
+else
+    grep "$tmpfile:2:3:.*missing.* initializers" "$errorfile"
+fi