Added `:both` support for forward_port protocol configuration

virtualbox_4_1.rb.patch

--- virtualbox_4_1.rb.orig	2012-09-09 01:24:56.000000000 +0800
+++ virtualbox_4_1.rb	2012-09-09 01:39:32.000000000 +0800
@@ -135,15 +135,22 @@
       def forward_ports(ports)
         args = []
         ports.each do |options|
-          pf_builder = [options[:name],
-                        options[:protocol] || "tcp",
-                        "",
-                        options[:hostport],
-                        "",
-                        options[:guestport]]
+          protocols = {
+            :both => ["tcp", "udp"],
+            :tcp  => ["tcp"],
+            :udp  => ["udp"]
+          }
+          protocols[options[:protocol] || :tcp].each do |protocol|
+            pf_builder = [protocol + options[:name],
+                          protocol,
+                          "",
+                          options[:hostport],
+                          "",
+                          options[:guestport]]
 
-          args.concat(["--natpf#{options[:adapter] || 1}",
-                       pf_builder.join(",")])
+            args.concat(["--natpf#{options[:adapter] || 1}",
+                         pf_builder.join(",")])
+          end
         end
 
         execute("modifyvm", @uuid, *args) if !args.empty?