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/lua/package.py

@@ -0,0 +1,26 @@
+from spack import *
+import os
+
+class Lua(Package):
+    """ The Lua programming language interpreter and library """
+    homepage = "http://www.lua.org"
+    url      = "http://www.lua.org/ftp/lua-5.1.5.tar.gz"
+
+    version('5.3.1', '797adacada8d85761c079390ff1d9961')
+    version('5.3.0', 'a1b0a7e92d0c85bbff7a8d27bf29f8af')
+    version('5.2.4', '913fdb32207046b273fdb17aad70be13')
+    version('5.2.3', 'dc7f94ec6ff15c985d2d6ad0f1b35654')
+    version('5.2.2', 'efbb645e897eae37cad4344ce8b0a614')
+    version('5.2.1', 'ae08f641b45d737d12d30291a5e5f6e3')
+    version('5.2.0', 'f1ea831f397214bae8a265995ab1a93e')
+    version('5.1.5', '2e115fe26e435e33b0d5c022e4490567')
+    version('5.1.4', 'd0870f2de55d59c1c8419f36e8fac150')
+    version('5.1.3', 'a70a8dfaa150e047866dc01a46272599')
+
+    depends_on('ncurses')
+
+    def install(self, spec, prefix):
+        make('INSTALL_TOP=%s' % prefix,
+             'MYLDFLAGS=-L%s/lib' % spec['ncurses'].prefix,
+             'linux',
+             'install')