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/hypre/package.py

@@ -0,0 +1,32 @@
+from spack import *
+
+class Hypre(Package):
+    """Hypre is a library of high performance preconditioners that
+       features parallel multigrid methods for both structured and
+       unstructured grid problems."""
+
+    homepage = "https://computation.llnl.gov/project/linear_solvers/software.php"
+    url      = "https://computation.llnl.gov/project/linear_solvers/download/hypre-2.10.0b.tar.gz"
+
+    version('2.10.0b', '768be38793a35bb5d055905b271f5b8e')
+
+    depends_on("mpi")
+    depends_on("blas")
+    depends_on("lapack")
+
+    def install(self, spec, prefix):
+        blas_dir = spec['blas'].prefix
+        lapack_dir = spec['lapack'].prefix
+
+        # Hypre's source is staged under ./src so we'll have to manually
+        # cd into it.
+        with working_dir("src"):
+            configure(
+                "--prefix=%s" % prefix,
+                "--with-blas-libs=blas",
+                "--with-blas-lib-dirs=%s/lib" % blas_dir,
+                "--with-lapack-libs=\"lapack blas\"",
+                "--with-lapack-lib-dirs=%s/lib" % lapack_dir,
+                "--with-MPI")
+            make()
+            make("install")