ENV.userpaths! Hotfix to prefer brewed stuff

The depends_on 'nose' => :python

tests fails even if people did `pip install nose`
with their brewed pythons because during
the tests the PATH is set up such that
/usr/bin comes before HOMEBRE_PREFIX/bin.

This is a hot fix. Proper fix need resorting
the PATH.

Library/Homebrew/extend/ENV.rb

@@ -440,6 +440,8 @@ class << ENV
   def userpaths!
     paths = ORIGINAL_PATHS.map { |p| p.realpath.to_s rescue nil } - %w{/usr/X11/bin /opt/X11/bin}
     self['PATH'] = paths.unshift(*self['PATH'].split(":")).uniq.join(":")
+    # XXX hot fix to prefer brewed stuff (e.g. python) over /usr/bin.
+    prepend 'PATH', HOMEBREW_PREFIX/'bin', ':'
   end
 
   def with_build_environment