New, cleaner package repository structure.

Package repositories now look like this:

    top-level-dir/
        repo.yaml
        packages/
            libelf/
                package.py
            mpich/
                package.py
            ...

This leaves room at the top level for additional metadata, source,
per-repo configs, indexes, etc., and it makes it easy to see that
something is a spack repo (just look for repo.yaml and packages).

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

@@ -0,0 +1,26 @@
+from spack import *
+
+class Elfutils(Package):
+    """elfutils is a collection of various binary tools such as
+    eu-objdump, eu-readelf, and other utilities that allow you to
+    inspect and manipulate ELF files. Refer to Table 5.Tools Included
+    in elfutils for Red Hat Developer for a complete list of binary
+    tools that are distributed with the Red Hat Developer Toolset
+    version of elfutils."""
+
+    homepage = "https://fedorahosted.org/elfutils/"
+
+    version('0.163',
+            git='git://git.fedorahosted.org/git/elfutils.git',
+            tag='elfutils-0.163')
+
+    provides('elf')
+
+    def install(self, spec, prefix):
+        autoreconf = which('autoreconf')
+        autoreconf('-if')
+
+        configure('--prefix=%s' % prefix, '--enable-maintainer-mode')
+        make()
+        make("install")
+