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/binutils/package.py

@@ -0,0 +1,30 @@
+from spack import *
+
+class Binutils(Package):
+    """GNU binutils, which contain the linker, assembler, objdump and others"""
+    homepage = "http://www.gnu.org/software/binutils/"
+    url      = "ftp://ftp.gnu.org/gnu/binutils/binutils-2.25.tar.bz2"
+
+    version('2.25', 'd9f3303f802a5b6b0bb73a335ab89d66')
+    version('2.24', 'e0f71a7b2ddab0f8612336ac81d9636b')
+    version('2.23.2', '4f8fa651e35ef262edc01d60fb45702e')
+    version('2.20.1', '2b9dc8f2b7dbd5ec5992c6e29de0b764')
+
+    variant('libiberty', default=False, description='Also install libiberty.')
+
+    def install(self, spec, prefix):
+        configure_args = [
+            '--prefix=%s' % prefix,
+            '--disable-dependency-tracking',
+            '--enable-interwork',
+            '--enable-multilib',
+            '--enable-shared',
+            '--enable-64-bit-bfd',
+            '--enable-targets=all']
+
+        if '+libiberty' in spec:
+            configure_args.append('--enable-install-libiberty')
+
+        configure(*configure_args)
+        make()
+        make("install")