Test for explitily setting layout true

See #727

If the default options for a template include :layout => false, it
should be possible to override this in the explicit options to the
rendering method.

e.g.

    set :slim, :layout => false

    get '/' do
      slim :index, :layout => true # should render with layout
    end

test/templates_test.rb

@@ -79,6 +79,21 @@ class TemplatesTest < Test::Unit::TestCase
     assert_equal "Hello World!", body
   end
 
+  it 'allows overriding false default layout with explicit true' do
+    mock_app do
+      template(:layout) { 'Layout!!! <%= yield %>' }
+      set :erb, :layout => false
+
+      get('/') do
+        erb('Hello World!', { :layout => true })
+      end
+    end
+
+    get '/'
+    assert ok?
+    assert_equal "Layout!!! Hello World!", body
+  end
+
   it 'renders String templates directly' do
     render_app { render(:test, 'Hello World') }
     assert ok?