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-numexpr/package.py

@@ -0,0 +1,15 @@
+from spack import *
+import re
+
+class PyNumexpr(Package):
+    """Fast numerical expression evaluator for NumPy"""
+    homepage = "https://pypi.python.org/pypi/numexpr"
+    url      = "https://pypi.python.org/packages/source/n/numexpr/numexpr-2.4.6.tar.gz"
+
+    version('2.4.6', '17ac6fafc9ea1ce3eb970b9abccb4fbd')
+
+    extends('python')
+    depends_on('py-numpy')
+
+    def install(self, spec, prefix):
+        python('setup.py', 'install', '--prefix=%s' % prefix)