There is no possibility to use subdir for templates in template store.

All templates have to be placed in flat template store. If you have many
templates this may be a problem. 

The attached patch allow to use subdir in template store. For example,
with this patch you can use "issue?@template=mobile/index" URL for
"mobile/issue.index.html" template.

This feature turned on for Jinja2 template. 

P.S. The patch is not so elegant as it can be. This is because of
(name,view) -> template_filename logic was moved from template engine logic:

 Template selection code is moved from Loader classes into cgi.client
 limiting the responsibility of Loaders to compilation and rendering.
 Internally, templating.find_template is replaced with
 client.selectTemplate.

I don't know the the reason of this decision.