Blacklist setuptools in favor of distribute.

Library/Homebrew/brew.h.rb

@@ -18,6 +18,14 @@ def check_for_blacklisted_formula names
       Mercurial can be install thusly:
         brew install pip && pip install mercurial
     EOS
+
+    when 'setuptools' then abort <<-EOS.undent
+      When working with a Homebrew-built Python, distribute is preferred
+      over setuptools, and can be used as the prequisite for pip.
+
+      Install distribute using:
+        brew install distribute
+    EOS
     end
   end
 end