Isolate LogicalFS/Container internals from the rest of the PLFS code.
Long term goal is to not have stuff outside of LogicalFS/Container
including files from here (e.g. Container.h).

details:
 - FileOp.cpp uses DT_CONTAINER but isn't in Container area, this
   should be cleaned up later.
 - currently removing all container code from tree and leaving
   a dummy stub there that returns ENOTSUP.  i'll add it back in
   as I get the index code restructured.
 - move hashValue out of Container and into Util.
 - FlatFileFD_FS --- use Util hashValue.
 - SmallFile shouldn't include Container.h and should use Util hashValue
 - Util traverseDirectoryTree moves to container since it knows about
   Metalinks and neither FlatFile nor SmallFile use it
 - mkdir_dash_p hardwired to use CONTAINER_MODE.   make it a param instead
 - move defn of DT_CONTAINER to plfs_private.h (XXX: would be nice to
   come back and isolate this better)
 - plfs_flatten_index tool uses internal Container APIs, redirect it
   to a more general API
 - plfs_ls, plfs_map, and plfs_version shouldn't include Container.h