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/repos/builtin/packages/libtool/package.py

@@ -0,0 +1,15 @@
+from spack import *
+
+class Libtool(Package):
+    """libtool -- library building part of autotools"""
+    homepage = "https://www.gnu.org/software/libtool/"
+    url      = "http://ftpmirror.gnu.org/libtool/libtool-2.4.2.tar.gz"
+
+    version('2.4.6' , 'addf44b646ddb4e3919805aa88fa7c5e')
+    version('2.4.2' , 'd2f3b7d4627e69e13514a40e72a24d50')
+
+    def install(self, spec, prefix):
+        configure("--prefix=%s" % prefix)
+
+        make()
+        make("install")