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/task/package.py

@@ -0,0 +1,20 @@
+from spack import *
+
+class Task(Package):
+    """Feature-rich console based todo list manager"""
+    homepage = "http://www.taskwarrior.org"
+    url      = "http://taskwarrior.org/download/task-2.4.4.tar.gz"
+
+    version('2.4.4', '517450c4a23a5842df3e9905b38801b3')
+
+    depends_on("gnutls")
+    depends_on("libuuid")
+    # depends_on("gcc@4.8:")
+
+    def install(self, spec, prefix):
+        with working_dir('spack-build', create=True):
+            cmake('-DCMAKE_BUILD_TYPE=release',
+                  '..',
+                  *std_cmake_args)
+            make()
+            make("install")