lib/pp.rb (Kernel#pp): Fix a race condition

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60948 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/pp.rb

@@ -17,13 +17,14 @@ module Kernel
   # prints arguments in pretty form.
   #
   # pp returns argument(s).
-  undef pp if method_defined?(:pp)
+  alias __pp_backup__ pp if method_defined?(:pp)
   def pp(*objs)
     objs.each {|obj|
       PP.pp(obj)
     }
     objs.size <= 1 ? objs.first : objs
   end
+  undef __pp_backup__ if method_defined?(:__pp_backup__)
   module_function :pp
 end