scheduling_poll#show raise an error if db is sqlite

[cat-in-136]

SQLite does not a native datetime type. COALESCE function call returns a string not datetime.

<% ((@poll.votes.group(:user).maximum("COALESCE(scheduling_votes.updated_at, scheduling_votes.created_at)").to_a) +
    (@poll.scheduling_poll_items.map{|v| [v, v.updated_at || v.created_at]} )).reject{|v| v[1].nil? }.sort{|a,b| a[1] <=> b[1]}.each do |v| %>
  <% subject, datetime = v %>
  <% if subject.kind_of? User
     user = subject %>
    <li>
      <%= avatar(user, :size => "24") %>
      <%= authoring datetime, user, :label => :label_updated_time_by %>
    </li>
  <% elsif subject.kind_of? SchedulingPollItem %>
    <li class="scheduling-poll-item-update">
      <%= l(:label_scheduling_poll_item) %> "<%=h subject.text %>":
      <%= l(:label_updated_time, :value => time_tag(datetime)).html_safe %>
    </li>
  <% end %>
<% end %>

authoring function 1st argument should be an DateTimeTimeZone but actual is a String if the DB is sqlite. In which case, an error raised.