Update //third_party/protobuf to version 3.

third_party/protobuf/ruby/Rakefile

+require "rubygems"
+require "rubygems/package_task"
+require "rake/extensiontask" unless RUBY_PLATFORM == "java"
+require "rake/testtask"
+
+spec = Gem::Specification.load("google-protobuf.gemspec")
+
+if RUBY_PLATFORM == "java"
+  if `which mvn` == ''
+    raise ArgumentError, "maven needs to be installed"
+  end
+  task :clean do
+    system("mvn clean")
+  end
+
+  task :compile do
+    system("mvn package")
+  end
+else
+  Rake::ExtensionTask.new("protobuf_c", spec) do |ext|
+    ext.ext_dir = "ext/google/protobuf_c"
+    ext.lib_dir = "lib/google"
+  end
+end
+
+Gem::PackageTask.new(spec) do |pkg|
+end
+
+Rake::TestTask.new(:test => :build) do |t|
+  t.test_files = FileList["tests/*.rb"]
+end
+
+task :build => [:clean, :compile]
+task :default => [:build]
+
+# vim:sw=2:et