Merge branch 'mplegendre-multi_pkgsrc_roots' into develop

- This moves var/spack/packages to var/spack/repos/builtin/packages.

- Packages that did not exist in the source branch, or were changed in
  develop, were moved into var/spack/repos/builtin/packages as part of
  the integration.

Conflicts:
	lib/spack/spack/test/unit_install.py
	var/spack/repos/builtin/packages/clang/package.py

var/spack/mock_configs/site_spackconfig/compilers.yaml

@@ -1,12 +0,0 @@
-compilers:
-  all:
-    clang@3.3:
-      cc: /path/to/clang
-      cxx: /path/to/clang++
-      f77: None
-      fc: None
-    gcc@4.5.0:
-      cc: /path/to/gcc
-      cxx: /path/to/g++
-      f77: /path/to/gfortran
-      fc: /path/to/gfortran

var/spack/repos/builtin.mock/repo.yaml

@@ -0,0 +1,2 @@
+repo:
+  namespace: builtin.mock

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

@@ -6,7 +6,7 @@
 # Written by Todd Gamblin, tgamblin@llnl.gov, All rights reserved.
 # LLNL-CODE-647188
 #
-# For details, see https://scalability-llnl.github.io/spack
+# For details, see https://llnl.github.io/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