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-periodictable/package.py

@@ -0,0 +1,17 @@
+from spack import *
+
+class PyPeriodictable(Package):
+    """nose extends the test loading and running features of unittest,
+    making it easier to write, find and run tests."""
+
+    homepage = "https://pypi.python.org/pypi/periodictable"
+    url      = "https://pypi.python.org/packages/source/p/periodictable/periodictable-1.4.1.tar.gz"
+
+    version('1.4.1', '7246b63cc0b6b1be6e86b6616f9e866e')
+
+    depends_on('py-numpy')
+    depends_on('py-pyparsing')
+    extends('python')
+
+    def install(self, spec, prefix):
+        python('setup.py', 'install', '--prefix=%s' % prefix)