Don't cast raw frame content to QString

The conversion is lossy and drops non-ASCII characters.

Fixes #503.

spec/driver_spec.rb

@@ -301,6 +301,24 @@ describe Capybara::Webkit::Driver do
     end
   end
 
+  context "binary content app" do
+    let(:driver) do
+      driver_for_app do
+        get '/' do
+          headers 'Content-Type' => 'application/octet-stream'
+          "Hello\xFF\xFF\xFF\xFFWorld"
+        end
+      end
+    end
+
+    before { visit("/") }
+
+    it "should return the binary content" do
+      src = driver.html.force_encoding('binary')
+      src.should == "Hello\xFF\xFF\xFF\xFFWorld".force_encoding('binary')
+    end
+  end
+
   context "hello app" do
     let(:driver) do
       driver_for_html(<<-HTML)

src/body.cpp

@@ -6,11 +6,8 @@ Body::Body(WebPageManager *manager, QStringList &arguments, QObject *parent) : S
 }
 
 void Body::start() {
-  QString result;
   if (page()->contentType().contains("html"))
-    result = page()->currentFrame()->toHtml();
+    finish(true, page()->currentFrame()->toHtml());
   else
-    result = page()->body();
-
-  finish(true, result);
+    finish(true, page()->body());
 }