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/py-pbr/package.py

@@ -0,0 +1,18 @@
+from spack import *
+import os
+
+class PyPbr(Package):
+    """PBR is a library that injects some useful and sensible default behaviors into your setuptools run."""
+    homepage = "https://pypi.python.org/pypi/pbr"
+    url      = "https://pypi.python.org/packages/source/p/pbr/pbr-1.8.1.tar.gz"
+
+    version('1.8.1', 'c8f9285e1a4ca6f9654c529b158baa3a')
+
+    extends('python')
+
+    depends_on('py-setuptools')
+
+    def install(self, spec, prefix):
+        python('setup.py', 'install', '--prefix=%s' % prefix)
+
+