relicense: replace LGPL headers with Apache-2.0/MIT SPDX headers

- remove the old LGPL license headers from all files in Spack
- add SPDX headers to all files
  - core and most packages are (Apache-2.0 OR MIT)
  - a very small number of remaining packages are LGPL-2.1-only

share/spack/csh/pathadd.csh

@@ -1,3 +1,8 @@
+# Copyright 2013-2018 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
 ########################################################################
 # Prepends directories to path, if they exist.
 #      pathadd /path/to/dir            # add to PATH

share/spack/csh/spack.csh

@@ -1,3 +1,8 @@
+# Copyright 2013-2018 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
 ########################################################################
 # This is a wrapper around the spack command that forwards calls to
 # 'spack use' and 'spack unuse' to shell functions.  This in turn