Fix daemonize behavior broken since 1.0.1

[Andrew Bortz <andrew.bortz@gmail.com>]

When rackup is run in daemonize mode, it fails to read the default
config file. In fact, it accepts a config file argument, but unless
that argument is an absolute path, it will also fail to load. The best
way I can think of to fix that is to resolve the absolute path of the
config file before the server is forked off (and chdir's to '/').

- Andrew

diff --git a/lib/rack/server.rb b/lib/rack/server.rb
index 8ef973c..edec62b 100644
--- a/lib/rack/server.rb
+++ b/lib/rack/server.rb
@@ -226,6 +226,7 @@ module Rack
        args.clear if ENV.include?("REQUEST_METHOD")

        options.merge! opt_parser.parse! args
+        options[:config] = ::File.expand_path(options[:config])
        ENV["RACK_ENV"] = options[:environment]
        options
      end