python3: install flat setuptools, pip

Avoid installing eggs to avoid problems with multiple installed
versions.

Formula/python3.rb

@@ -207,12 +207,15 @@ class Python3 < Formula
     # setuptools-0.9.8-py3.3.egg
     rm_rf Dir["#{site_packages}/setuptools*"]
     rm_rf Dir["#{site_packages}/distribute*"]
+    rm_rf Dir["#{site_packages}/pip[-_.][0-9]*", "#{site_packages}/pip"]
 
     %w[setuptools pip].each do |pkg|
       (libexec/pkg).cd do
         system bin/"python3", "-s", "setup.py", "--no-user-cfg", "install",
                "--force", "--verbose", "--install-scripts=#{bin}",
-               "--install-lib=#{site_packages}"
+               "--install-lib=#{site_packages}",
+               "--single-version-externally-managed",
+               "--record=installed.txt"
       end
     end