fix leaked fds

* lib/rubygems/command.rb (Gem::Command#invoke_with_build_args):
  restore UI and close the created SilentUI.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@61465 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/rubygems/command.rb

@@ -300,7 +300,10 @@ class Gem::Command
 
     options[:build_args] = build_args
 
-    self.ui = Gem::SilentUI.new if options[:silent]
+    if options[:silent]
+      old_ui = self.ui
+      self.ui = ui = Gem::SilentUI.new
+    end
 
     if options[:help] then
       show_help
@@ -309,6 +312,11 @@ class Gem::Command
     else
       execute
     end
+  ensure
+    if ui
+      self.ui = old_ui
+      ui.close
+    end
   end
 
   ##