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/harfbuzz/package.py

@@ -0,0 +1,20 @@
+from spack import *
+
+class Harfbuzz(Package):
+    """The Harfbuzz package contains an OpenType text shaping engine."""
+    homepage = "http://www.freedesktop.org/wiki/Software/HarfBuzz/"
+    url      = "http://www.freedesktop.org/software/harfbuzz/release/harfbuzz-0.9.37.tar.bz2"
+
+    version('0.9.37', 'bfe733250e34629a188d82e3b971bc1e')
+
+    depends_on("glib")
+    depends_on("icu")
+    depends_on("freetype")
+
+    def patch(self):
+        change_sed_delimiter('@', ';', 'src/Makefile.in')
+
+    def install(self, spec, prefix):
+        configure("--prefix=%s" % prefix)
+        make()
+        make("install")