Fix rack driver to support buttons with no 'type' attribute

(type defaults to 'submit' according to HTML 4/5 specs)

lib/capybara/driver/rack_test_driver.rb

@@ -70,7 +70,8 @@ class Capybara::Driver::RackTest < Capybara::Driver::Base
       if tag_name == 'a'
         method = self["data-method"] || :get
         driver.process(method, self[:href].to_s)
-      elsif (tag_name == 'input' or tag_name == 'button') and %w(submit image).include?(type)
+      elsif (tag_name == 'input' and %w(submit image).include?(type)) or
+          ((tag_name == 'button') and type.nil? or type == "submit")
         Form.new(driver, form).submit(self)
       end
     end

lib/capybara/spec/session/click_link_or_button_spec.rb

@@ -12,6 +12,12 @@ shared_examples_for "click_link_or_button" do
       extract_results(@session)['first_name'].should == 'John'
     end
 
+    it "should click on a button with no type attribute" do
+      @session.visit('/form')
+      @session.click_link_or_button('no_type')
+      extract_results(@session)['first_name'].should == 'John'
+    end
+
     it "should be aliased as click for backward compatibility" do
       Capybara.should_receive(:deprecate).with("click", "click_link_or_button")
       @session.visit('/form')

lib/capybara/spec/views/form.erb

@@ -217,6 +217,7 @@
     <input type="image" name="form[okay]" id="okay556" value="okay" alt="oh hai thar"/>
     <button type="submit" id="click_me_123" value="click_me">Click me!</button>
     <button type="submit" name="form[no_value]">No Value!</button>
+    <button id="no_type">No Type!</button>
   </p>
 </form>