Adds requirements for Fedora's alpha-6 implementation of LDP.

Uses PUT/POST appropriately for creating a new record with an ID.
A resource is defined by LDP#DirectContainer
Updates etag and last-modified in cached response when updating - stops
412 errors on repeated saves.
If I revert this then responses from Fedora 4 won't be wrapped, because it just sends LDP.direct_container as the type for resources.