webrick: allow shutdown after StartCallback

We must to ensure the @status ivar is set to :Running before
running StartCallback, otherwise Webrick::Server#stop will not
change the @status to :Shutdown properly.

Note: I have not been able to reproduce the original issue but
understood at least part of the problem and fixed it with this
commit.  However, the original reporter (Peak Xu) was still able
to reproduce the problem on 1.9.2 p180 on Windows, so I'm not
sure what else might be going on.  Ruby threading and
synchronization primitives have changed a lot since 1.9.2, so
maybe that was fixed elsewhere.

* lib/webrick/server.rb: call StartCallback sooner [Bug #4841]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@61083 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/webrick/server.rb

@@ -157,12 +157,12 @@ module WEBrick
       server_type.start{
         @logger.info \
           "#{self.class}#start: pid=#{$$} port=#{@config[:Port]}"
+        @status = :Running
         call_callback(:StartCallback)
 
         shutdown_pipe = @shutdown_pipe
 
         thgroup = ThreadGroup.new
-        @status = :Running
         begin
           while @status == :Running
             begin