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/mpe2/mpe2.patch

@@ -0,0 +1,12 @@
+diff -rupN mpe2-1.3.0/src/graphics/src/mpe_graphics.c mpe2-1.3.0.new/src/graphics/src/mpe_graphics.c
+--- mpe2-1.3.0/src/graphics/src/mpe_graphics.c	2009-06-15 10:36:22.000000000 -0600
++++ mpe2-1.3.0.new/src/graphics/src/mpe_graphics.c	2014-10-25 00:11:22.000000000 -0600
+@@ -982,7 +982,7 @@ char *string;
+     return MPE_ERR_BAD_ARGS;
+   }
+ 
+-  printf("color = %d, string = %s\n",(int) color, string);
++//printf("color = %d, string = %s\n",(int) color, string);
+ 
+   XBSetPixVal( graph->xwin, graph->xwin->cmapping[color] );
+   returnVal = XDrawString( graph->xwin->disp, XBDrawable(graph->xwin),

var/spack/repos/builtin/packages/mpe2/package.py

@@ -0,0 +1,28 @@
+from spack import *
+
+class Mpe2(Package):
+    """Message Passing Extensions (MPE) -- Parallel, shared X window graphics"""
+
+    homepage = "http://www.mcs.anl.gov/research/projects/perfvis/software/MPE/"
+    url      = "ftp://ftp.mcs.anl.gov/pub/mpi/mpe/mpe2-1.3.0.tar.gz"
+
+    version('1.3.0', '67bf0c7b2e573df3ba0d2059a96c2f7b')
+
+    patch('mpe2.patch')
+
+    depends_on("mpi")
+
+    provides("mpe")
+
+    def install(self, spec, prefix):
+        configure("--prefix=" + prefix,
+                  "--x-includes=/usr/X11R6/include",
+                  "--x-libraries=/usr/X11R6/lib",
+                  "--enable-mpe_graphics=yes",
+                  "--disable-f77",
+                  "--enable-viewers=no",
+                  "--enable-slog2=no",
+                  "--with-mpicc=mpicc")
+
+        make()
+        make("install")