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/dbus/package.py

@@ -0,0 +1,31 @@
+from spack import *
+
+class Dbus(Package):
+    """D-Bus is a message bus system, a simple way for applications to
+       talk to one another. D-Bus supplies both a system daemon (for
+       events such new hardware device printer queue ) and a
+       per-user-login-session daemon (for general IPC needs among user
+       applications). Also, the message bus is built on top of a
+       general one-to-one message passing framework, which can be used
+       by any two applications to communicate directly (without going
+       through the message bus daemon)."""
+
+    homepage = "http://dbus.freedesktop.org/"
+    url      = "http://dbus.freedesktop.org/releases/dbus/dbus-1.8.8.tar.gz"
+
+    version('1.9.0', 'ec6895a4d5c0637b01f0d0e7689e2b36')
+    version('1.8.8', 'b9f4a18ee3faa1e07c04aa1d83239c43')
+    version('1.8.6', '6a08ba555d340e9dfe2d623b83c0eea8')
+    version('1.8.4', '4717cb8ab5b80978fcadf2b4f2f72e1b')
+    version('1.8.2', 'd6f709bbec0a022a1847c7caec9d6068')
+
+    def install(self, spec, prefix):
+        configure(
+            "--prefix=%s" % prefix,
+            "--disable-systemd")
+        make()
+        make("install")
+
+        # dbus needs a machine id generated after install
+        dbus_uuidgen = Executable(join_path(prefix.bin, 'dbus-uuidgen'))
+        dbus_uuidgen('--ensure')