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/geos/package.py

@@ -0,0 +1,31 @@
+from spack import *
+
+class Geos(Package):
+    """GEOS (Geometry Engine - Open Source) is a C++ port of the Java
+       Topology Suite (JTS). As such, it aims to contain the complete
+       functionality of JTS in C++. This includes all the OpenGIS
+       Simple Features for SQL spatial predicate functions and spatial
+       operators, as well as specific JTS enhanced topology functions."""
+
+    homepage = "http://trac.osgeo.org/geos/"
+    url      = "http://download.osgeo.org/geos/geos-3.4.2.tar.bz2"
+
+    version('3.4.2', 'fc5df2d926eb7e67f988a43a92683bae')
+    version('3.4.1', '4c930dec44c45c49cd71f3e0931ded7e')
+    version('3.4.0', 'e41318fc76b5dc764a69d43ac6b18488')
+    version('3.3.9', '4794c20f07721d5011c93efc6ccb8e4e')
+    version('3.3.8', '75be476d0831a2d14958fed76ca266de')
+    version('3.3.7', '95ab996d22672b067d92c7dee2170460')
+    version('3.3.6', '6fadfb941541875f4976f75fb0bbc800')
+    version('3.3.5', '2ba61afb7fe2c5ddf642d82d7b16e75b')
+    version('3.3.4', '1bb9f14d57ef06ffa41cb1d67acb55a1')
+    version('3.3.3', '8454e653d7ecca475153cc88fd1daa26')
+
+    extends('python')
+    depends_on('swig')
+
+    def install(self, spec, prefix):
+        configure("--prefix=%s" % prefix,
+                  "--enable-python")
+        make()
+        make("install")