vcs.rb: suppress warning

* tool/vcs.rb (DebugPOpen): suppress refinements warning in 2.0.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@56658 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

tool/vcs.rb

@@ -79,12 +79,15 @@ if RUBY_VERSION < "2.0"
   end
 else
   module DebugPOpen
+    verbose, $VERBOSE = $VERBOSE, nil if RUBY_VERSION < "2.1"
     refine IO.singleton_class do
       def popen(*args)
         STDERR.puts args.inspect if $DEBUG
         super
       end
     end
+  ensure
+    $VERBOSE = verbose unless verbose.nil?
   end
   using DebugPOpen
 end