IResource:
  Add site to interface (it's in Resource)

ISite:
  Create ISite interface
  Add locateSiblingResource()? (I have it in DAVFile, which is an IResource)

IDAVResource:
  Create IDAVResource interface

Integrate authentication configuration into DAV methods.

Most HTTP preconditions up to Resource.
pre/post conditions per method (see deltaV)

Figure out how to do logging without hacking renderHTTP()
