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/arpack/package.py

@@ -0,0 +1,41 @@
+from spack import *
+import os
+import shutil
+
+class Arpack(Package):
+    """A collection of Fortran77 subroutines designed to solve large scale
+       eigenvalue problems.
+    """
+    homepage = "http://www.caam.rice.edu/software/ARPACK/"
+    url      = "http://www.caam.rice.edu/software/ARPACK/SRC/arpack96.tar.gz"
+
+    version('96', 'fffaa970198b285676f4156cebc8626e')
+
+    depends_on('blas')
+    depends_on('lapack')
+
+    def patch(self):
+        # Filter the cray makefile to make a spack one.
+        shutil.move('ARMAKES/ARmake.CRAY', 'ARmake.inc')
+        makefile = FileFilter('ARmake.inc')
+
+        # Be sure to use Spack F77 wrapper
+        makefile.filter('^FC.*', 'FC = f77')
+        makefile.filter('^FFLAGS.*', 'FFLAGS = -O2 -g')
+
+        # Set up some variables.
+        makefile.filter('^PLAT.*',      'PLAT = ')
+        makefile.filter('^home.*',    'home = %s' % os.getcwd())
+        makefile.filter('^BLASdir.*',   'BLASdir = %s' % self.spec['blas'].prefix)
+        makefile.filter('^LAPACKdir.*', 'LAPACKdir = %s' % self.spec['lapack'].prefix)
+
+        # build the library in our own prefix.
+        makefile.filter('^ARPACKLIB.*', 'ARPACKLIB = %s/libarpack.a' % os.getcwd())
+
+
+    def install(self, spec, prefix):
+        with working_dir('SRC'):
+            make('all')
+
+        mkdirp(prefix.lib)
+        install('libarpack.a', prefix.lib)