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/cscope/package.py

@@ -0,0 +1,17 @@
+from spack import *
+
+class Cscope(Package):
+    """Cscope is a developer's tool for browsing source code."""
+    homepage = "http://http://cscope.sourceforge.net/"
+    url      = "http://downloads.sourceforge.net/project/cscope/cscope/15.8b/cscope-15.8b.tar.gz"
+
+    version('15.8b', '8f9409a238ee313a96f9f87fe0f3b176')
+
+    # Can be configured to use flex (not necessary)
+    # ./configure --with-flex
+
+    def install(self, spec, prefix):
+        configure('--prefix=%s' % prefix)
+
+        make()
+        make("install")