mkpath all directories under lib/python*

The python formula explicity creates lib/python2.7/site-packages.
However, that path may already exist as a symlink if something that
installs python bindings is installed before python itself. The result
is that some random keg will end up hosting the site-packages directory
instead of the top-level directory.

Fix this by explicitly creating directories under lib/python* during
linking.

Fixes Homebrew/homebrew#11882.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>

Library/Homebrew/keg.rb

@@ -97,7 +97,7 @@ class Keg < Pathname
       when /^ocaml/ then :mkpath
       when /^perl5/ then :mkpath
       when 'php' then :mkpath
-      when /^python[23]\.\d$/ then :mkpath
+      when /^python[23]\.\d/ then :mkpath
       when 'ruby' then :mkpath
       # Everything else is symlinked to the cellar
       else :link