Implement review requests

- use two empty lines before `class`
- change version numbering scheme for packages, use `url_for_version` to make things work
- specify dependency types
- add comment about temporarily moved download location
- update two packages to newer versions

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

@@ -26,14 +26,20 @@
 import shutil
 from spack import *
 
+
 class Nauty(Package):
     """nauty and Traces are programs for computing automorphism groups of
     graphsq and digraphs"""
     homepage = "http://pallini.di.uniroma1.it/index.html"
-    url      = "http://pallini.di.uniroma1.it/nauty26r5.tar.gz"
+    url      = "http://pallini.di.uniroma1.it/nauty26r7.tar.gz"
 
-    version('26r5', '91b03a7b069962e94fc9aac8831ce8d2')
-    version('25r9', 'e8ecd08b0892a1fb13329c147f08de6d')
+    def url_for_version(self, version):
+        return ("http://pallini.di.uniroma1.it/nauty%s.tar.gz" %
+                str(version).replace('.', ''))
+
+    version('2.6r7', 'b2b18e03ea7698db3fbe06c5d76ad8fe')
+    version('2.6r5', '91b03a7b069962e94fc9aac8831ce8d2')
+    version('2.5r9', 'e8ecd08b0892a1fb13329c147f08de6d')
 
     def install(self, spec, prefix):
         configure('--prefix=%s' % prefix)