webrick/server: simplify Daemon.start

Process.daemon exists since Ruby 1.9.1 and does most of what we need.

* lib/webrick/server.rb (Daemon.start): simplify
  [Misc #12937]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@56869 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/webrick/server.rb

@@ -44,14 +44,8 @@ module WEBrick
     # block, if given.
 
     def Daemon.start
-      exit!(0) if fork
-      Process::setsid
-      exit!(0) if fork
-      Dir::chdir("/")
-      File::umask(0)
-      STDIN.reopen(IO::NULL)
-      STDOUT.reopen(IO::NULL, "w")
-      STDERR.reopen(IO::NULL, "w")
+      Process.daemon
+      File.umask(0)
       yield if block_given?
     end
   end