Added a 'Assignable' boolean on Role model.

If unchecked, issues can not be assigned to users having this role.

git-svn-id: http://redmine.rubyforge.org/svn/trunk@649 e93f8b46-1217-0410-a6f0-8f06a7374b81

app/views/roles/_form.rhtml

@@ -2,6 +2,8 @@
 <div class="box">
 <!--[form:role]-->
 <p><%= f.text_field :name, :required => true %></p>
+<p><%= f.check_box :assignable %></p>
+<div class="clear"></div>
 
 <h3><%=l(:label_permissions)%></h3>
 <% permissions = @permissions.group_by {|p| p.group_id } %>