Do not lookup for hints if it was explicitly given false

After #405 we added hint classes for the wrappers, but this has forced the
loading of the hint text doing I18n lookups, even though it was explicitly
given false. This checks for the option in #has_hint?, avoiding the lookup
in such cases.

This issues has been caught after #627 and some further investigation,
thanks to @shwoodard.

lib/simple_form/components/hints.rb

@@ -11,7 +11,7 @@ module SimpleForm
       end
 
       def has_hint?
-        hint.present?
+        options[:hint] != false && hint.present?
       end
     end
   end

test/form_builder/general_test.rb

@@ -264,6 +264,8 @@ class FormBuilderTest < ActionView::TestCase
 
   test 'builder should be able to disable a hint even if it exists in i18n' do
     store_translations(:en, :simple_form => { :hints => { :name => 'Hint test' } }) do
+      SimpleForm::Inputs::Base.any_instance.expects(:hint).never
+
       with_form_for @user, :name, :hint => false
       assert_no_select 'span.hint'
     end