rubygems/util.rb: fix leaked FDs

* lib/rubygems/util.rb (silent_system): close duplicated IOs.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46945 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
specification.rb: fix leaked FDs

* lib/rubygems/specification.rb (build_extensions): close
  redirection FDs.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46946 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
rubygems/util.rb: redirect options

* lib/rubygems/util.rb (Gem.silent_system): use keyword options to
  redirect outputs instead of reopening global IOs.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46947 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
fix encoding spec

"UTF-8" is invalid encoding name in Emacs, use "utf-8" instead.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46948 b2dd03c8-39d4-4d8f-98ff-823fe69b080e