Only use custom_teaser if the migration has run

app/views/admin/blog/posts/_form.html.erb

@@ -38,7 +38,7 @@
                      :locals => {
                        :f => f,
                        :part_index => (part_index += 1),
-                     } -%>
+                     } if f.object.respond_to?(:custom_teaser) -%>
         <% Refinery::Blog.tabs.each_with_index do |tab, tab_index| %>
           <div class='page_part' id='<%= "custom_tab_#{tab_index}" %>'>
             <%= render :partial => tab.partial, :locals => {:f => f} %>