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/mesa/package.py

@@ -0,0 +1,34 @@
+from spack import *
+
+class Mesa(Package):
+    """Mesa is an open-source implementation of the OpenGL
+    specification - a system for rendering interactive 3D graphics."""
+
+    homepage = "http://www.mesa3d.org"
+    url      = "ftp://ftp.freedesktop.org/pub/mesa/older-versions/8.x/8.0.5/MesaLib-8.0.5.tar.gz"
+    # url      = "ftp://ftp.freedesktop.org/pub/mesa/10.4.4/MesaLib-10.4.4.tar.gz"
+
+    # version('10.4.4', '8d863a3c209bf5116b2babfccccc68ce')
+    version('8.0.5', 'cda5d101f43b8784fa60bdeaca4056f2')
+
+    # mesa 7.x, 8.x, 9.x
+    depends_on("libdrm@2.4.33")
+    depends_on("llvm@3.0")
+    depends_on("libxml2")
+
+    # patch("llvm-fixes.patch") # using newer llvm
+
+    # mesa 10.x
+    # depends_on("py-mako")
+    # depends_on("flex")
+    # depends_on("bison")
+    # depends_on("dri2proto")
+    # depends_on("libxcb")
+    # depends_on("libxshmfence")
+
+
+    def install(self, spec, prefix):
+        configure("--prefix=%s" % prefix)
+
+        make()
+        make("install")