sstephenson/sprockets — pull request #421 by doitian (2013-03-16 17:07:47+00:00)
Title: Change rack session options only when asset is found

If asset is not found, Rack will try next route since `X-Cascade` header
is set. It is better do not change env when the request is pass through.

[sporkd/asset_prefix_test](https://github.com/sporkd/asset_prefix_test)
has demonstrated that when assets prefix is also a prefix of controller
routes, the session is never stored.