externals: move spack.util.ordereddict to external/ordereddict_backport

lib/spack/external/_pytest/fixtures.py

@@ -21,10 +21,7 @@
 from _pytest.outcomes import fail, TEST_OUTCOME
 
 
-if sys.version_info[:2] == (2, 6):
-    from ordereddict import OrderedDict
-else:
-    from collections import OrderedDict  # nopyqver
+from ordereddict_backport import OrderedDict
 
 
 def pytest_sessionstart(session):

lib/spack/external/ordereddict_backport.py

@@ -0,0 +1,40 @@
+##############################################################################
+# Copyright (c) 2013-2018, 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/spack/spack
+# Please also see the NOTICE and LICENSE files 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
+##############################################################################
+"""This file dispatches to the correct implementation of OrderedDict."""
+
+# TODO: this file can be removed when support for python 2.6 will be dropped
+
+# Removing this import will make python 2.6
+# fail on import of ordereddict
+from __future__ import absolute_import
+
+import sys
+
+if sys.version_info[:2] == (2, 6):
+    import ordereddict
+    OrderedDict = ordereddict.OrderedDict
+else:
+    import collections
+    OrderedDict = collections.OrderedDict