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/boxlib/package.py

@@ -0,0 +1,25 @@
+from spack import *
+
+class Boxlib(Package):
+    """BoxLib, a software framework for massively parallel
+       block-structured adaptive mesh refinement (AMR) codes."""
+
+    homepage = "https://ccse.lbl.gov/BoxLib/"
+    url = "https://ccse.lbl.gov/pub/Downloads/BoxLib.git";
+
+    # TODO: figure out how best to version this.  No tags in the repo!
+    version('master', git='https://ccse.lbl.gov/pub/Downloads/BoxLib.git')
+
+    depends_on('mpi')
+
+    def install(self, spec, prefix):
+        args = std_cmake_args
+        args += ['-DCCSE_ENABLE_MPI=1',
+                 '-DCMAKE_C_COMPILER=%s' % which('mpicc'),
+                 '-DCMAKE_CXX_COMPILER=%s' % which('mpicxx'),
+                 '-DCMAKE_Fortran_COMPILER=%s' % which('mpif90')]
+
+        cmake('.', *args)
+        make()
+        make("install")
+