The monotonic clock is immune to system time changes and
a better option for implementing timing comparisons.

* lib/webrick/utils.rb (TimeoutHandler): use monotonic clock
  (watch): ditto

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@56417 b2dd03c8-39d4-4d8f-98ff-823fe69b080e