webrick: fix non-ascii escape bugs

* lib/webrick/htmlutils.rb (WEBrick::HTMLUtils#escape): replace HTML
  meta chars even in non-ascii string.  [Bug #8425] [ruby-core:55052]
* lib/webrick/httputils.rb (WEBrick::HTTPUtils#{_escape,_unescape}):
  fix %-escape encodings.  [Bug #8425] [ruby-core:55052]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40848 b2dd03c8-39d4-4d8f-98ff-823fe69b080e