Give explicit url option.

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@8464 e93f8b46-1217-0410-a6f0-8f06a7374b81

app/views/wiki/history.html.erb

@@ -4,7 +4,7 @@
 
 <h3><%= l(:label_history) %></h3>
 
-<% form_tag({:action => "diff"}, :method => :get) do %>
+<% form_tag({:controller => 'wiki', :action => 'diff', :project_id => @page.project, :id => @page.title}, :method => :get) do %>
 <table class="list wiki-page-versions">
 <thead><tr>
     <th>#</th>