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/lcms/package.py

@@ -0,0 +1,19 @@
+from spack import *
+
+class Lcms(Package):
+    """Little cms is a color management library. Implements fast
+       transforms between ICC profiles. It is focused on speed, and is
+       portable across several platforms (MIT license)."""
+    homepage = "http://www.littlecms.com"
+    url      = "http://downloads.sourceforge.net/project/lcms/lcms/2.6/lcms2-2.6.tar.gz"
+
+    version('2.6', 'f4c08d38ceade4a664ebff7228910a33')
+
+    depends_on("jpeg")
+    depends_on("libtiff")
+    depends_on("zlib")
+
+    def install(self, spec, prefix):
+        configure("--prefix=%s" % prefix)
+        make()
+        make("install")