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/cloog/package.py

@@ -0,0 +1,26 @@
+from spack import *
+
+class Cloog(Package):
+    """CLooG is a free software and library to generate code for
+    scanning Z-polyhedra. That is, it finds a code (e.g. in C,
+    FORTRAN...) that reaches each integral point of one or more
+    parameterized polyhedra."""
+
+    homepage = "http://www.cloog.org"
+    url      = "http://www.bastoul.net/cloog/pages/download/count.php3?url=./cloog-0.18.1.tar.gz"
+    list_url = "http://www.bastoul.net/cloog/pages/download"
+
+    version('0.18.1', 'e34fca0540d840e5d0f6427e98c92252')
+    version('0.18.0', 'be78a47bd82523250eb3e91646db5b3d')
+    version('0.17.0', '0aa3302c81f65ca62c114e5264f8a802')
+
+    depends_on("gmp")
+    depends_on("isl")
+
+    def install(self, spec, prefix):
+        configure("--prefix=%s" % prefix,
+                  "--with-osl=no",
+                  "--with-isl=%s" % spec['isl'].prefix,
+                  "--with-gmp=%s" % spec['gmp'].prefix)
+        make()
+        make("install")