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/bzip2/package.py

@@ -0,0 +1,36 @@
+from spack import *
+from glob import glob
+
+class Bzip2(Package):
+    """bzip2 is a freely available, patent free high-quality data
+       compressor. It typically compresses files to within 10% to 15%
+       of the best available techniques (the PPM family of statistical
+       compressors), whilst being around twice as fast at compression
+       and six times faster at decompression."""
+    homepage = "http://www.bzip.org"
+    url      = "http://www.bzip.org/1.0.6/bzip2-1.0.6.tar.gz"
+
+    version('1.0.6', '00b516f4704d4a7cb50a1d97e6e8e15b')
+
+    def install(self, spec, prefix):
+        # No configure system -- have to filter the makefile for this package.
+        filter_file(r'CC=gcc', 'CC=cc', 'Makefile', string=True)
+
+        make('-f', 'Makefile-libbz2_so')
+        make('clean')
+        make("install", "PREFIX=%s" % prefix)
+
+        bzip2_exe = join_path(prefix.bin, 'bzip2')
+        install('bzip2-shared', bzip2_exe)
+        for i, libfile in enumerate(glob('libbz2.so*')):
+            install(libfile, prefix.lib)
+            if i == 0:
+                symlink(join_path(prefix.lib, libfile), join_path(prefix.lib, 'libbz2.so'))
+
+        bunzip2 = join_path(prefix.bin, 'bunzip2')
+        remove(bunzip2)
+        symlink(bzip2_exe, bunzip2)
+
+        bzcat   = join_path(prefix.bin, 'bzcat')
+        remove(bzcat)
+        symlink(bzip2_exe, bzcat)