Add Package: IceT

Adds the IceT compositing library from Sandia/Kitware.
Most default functionality needed for image compositing is
added, OpenGL acceleration for very large displays is disabled.

Downstream usage:
  most VTK based software which supports parallel image compositing,
such as VisIt, Paraview and in our use-case
[ISAAC](https://github.com/ComputationalRadiationPhysics/isaac).

var/spack/repos/builtin/packages/icet/package.py

+##############################################################################
+# Copyright (c) 2013-2016, Lawrence Livermore National Security, LLC.
+# Produced at the Lawrence Livermore National Laboratory.
+#
+# This file is part of Spack.
+# Created by Todd Gamblin, tgamblin@llnl.gov, All rights reserved.
+# LLNL-CODE-647188
+#
+# For details, see https://github.com/llnl/spack
+# Please also see the LICENSE file for our notice and the LGPL.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License (as
+# published by the Free Software Foundation) version 2.1, February 1999.
+#
+# This program 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 terms and
+# conditions of the GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public
+# License along with this program; if not, write to the Free Software
+# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+##############################################################################
+from spack import *
+
+
+class Icet(CMakePackage):
+    """The Image Composition Engine for Tiles (IceT) is a high-performance
+       sort-last parallel rendering library."""
+
+    homepage = "http://icet.sandia.gov"
+    url = "https://example.com/icet-1.2.3.tar.gz"
+
+    version('develop', branch='master',
+            git='https://gitlab.kitware.com/icet/icet.git')
+    version('2.1.1', '4f971c51105a64937460d482adca2a6c')
+
+    depends_on('cmake', type='build')
+    depends_on('mpi')
+
+    def url_for_version(self, version):
+        return ("https://gitlab.kitware.com/icet/icet/repository/"
+                "archive.tar.bz2?ref=IceT-{0}".format(version.dotted))
+
+    def cmake_args(self):
+        return ['-DICET_USE_OPENGL:BOOL=OFF']