Support empty Time inputs

Before this change, it wasn't possible to create an input of type 'time'
that didn't default to the current date. This made it impossible to
differentiate between a form submission wherein the user hadn't picked a
date, and one in which they'd picked midnight UTC.

lib/formtastic/inputs/time_input.rb

@@ -15,12 +15,8 @@ def fragments
         time_fragments
       end
 
-      def value_or_default_value
-        value ? value : Time.current
-      end
-
       def fragment_value(fragment)
-        value_or_default_value.send(fragment)
+        value ? value.send(fragment) : ""
       end
 
       def hidden_fragments
@@ -43,4 +39,4 @@ def hidden_field_name(fragment)
 
     end
   end
-end
+end

spec/inputs/time_input_spec.rb

@@ -60,6 +60,33 @@
 
     end
 
+    describe "with :ignore_date => false and no initial Time" do
+      before do
+        @new_post.stub(:publish_at)
+        concat(semantic_form_for(@new_post) do |builder|
+          concat(builder.input(:publish_at, :as => :time, :ignore_date => false))
+        end)
+      end
+
+      it 'should have a hidden input for day, month and year' do
+        output_buffer.should have_tag('input#post_publish_at_1i')
+        output_buffer.should have_tag('input#post_publish_at_2i')
+        output_buffer.should have_tag('input#post_publish_at_3i')
+      end
+
+      it 'should not have values in hidden inputs for day, month and year' do
+        output_buffer.should have_tag('input#post_publish_at_1i[@value=""]')
+        output_buffer.should have_tag('input#post_publish_at_2i[@value=""]')
+        output_buffer.should have_tag('input#post_publish_at_3i[@value=""]')
+      end
+
+      it 'should have an select for hour and minute' do
+        output_buffer.should have_tag('select#post_publish_at_4i')
+        output_buffer.should have_tag('select#post_publish_at_5i')
+      end
+
+    end
+
     describe "without seconds" do
       before do
         concat(semantic_form_for(@new_post) do |builder|