fix cache invariant for grouped todos in context and project view

app/helpers/application_helper.rb

@@ -294,5 +294,9 @@ module ApplicationHelper
       })
   end
 
+  def source_view_key
+    # uses @project.id or @context.id depending on source_view
+    source_view_is_one_of(:project, :context) ? "#{@source_view}-#{eval("@#{@source_view}.id")}" : @source_view
+  end
 
 end

app/views/contexts/_context.html.erb

@@ -2,7 +2,7 @@
 @not_done = @not_done_todos.select {|t| t.context_id == context.id }
 # invalidate the cache every day because of staleness or
 # rendering of "due in x days" that change without touching updated at of the todo
-cache [context, @source_view, current_user.date.strftime("%Y%m%d"), @tag_name] do
+cache [context, source_view_key, current_user.date.strftime("%Y%m%d"), @tag_name] do
 -%>
   <%= 
     render :partial => 'todos/collection', 

app/views/projects/_project.html.erb

@@ -2,7 +2,7 @@
 @not_done = @not_done_todos.select {|t| t.project_id == project.id }
 # invalidate the cache every day because of staleness or
 # rendering of "due in x days" that change without touching updated at of the todo
-cache [project, @source_view, current_user.date.strftime("%Y%m%d"), @tag_name] do 
+cache [project, source_view_key, current_user.date.strftime("%Y%m%d"), @tag_name] do 
 -%>
   <%= 
     title = source_view_is(:project) ? t('projects.actions_in_project_title') : show_project_name(project)