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/readline/package.py

@@ -0,0 +1,21 @@
+from spack import *
+
+class Readline(Package):
+    """The GNU Readline library provides a set of functions for use by
+       applications that allow users to edit command li nes as they
+       are typed in. Both Emacs and vi editing modes are
+       available. The Readline library includes additional functions
+       to maintain a list of previously-entered command lines, to
+       recall and perhaps reedit those lines, and perform csh-like
+       history expansion on previous commands. """
+    homepage = "http://cnswww.cns.cwru.edu/php/chet/readline/rltop.html"
+    url      = "ftp://ftp.cwru.edu/pub/bash/readline-6.3.tar.gz"
+
+    version('6.3', '33c8fb279e981274f485fd91da77e94a')
+
+    depends_on("ncurses")
+
+    def install(self, spec, prefix):
+        configure("--prefix=%s" % prefix)
+        make("SHLIB_LIBS=-lncurses")
+        make("install")