* NodeFileSystem: interface for defining filesystems in terms of inodes.

* FsNode: interface for inodes to be used by NodeFileSystem

* PathNodeFs: NodeFileSystem that assumes bijective mapping between
  inodes and paths

* Change inode to Inode, a public (but mostly opaque) type.

Use inodeFs as layer between FileSystemConnector and FileSystem.

This further prepares fsInode as an intermediate layer between raw and
path filesystems.

Only fsInode maintains Parent links. This prepares for inserting
a layer between RawFileSystem and FileSystem, which can define
filesystems in terms of inodes.

rm from coreutils < 8.0 is relying on synchronization between a read
of and unlink within a directory.  Posix does not require such
synchronization.

For making the test pass, install coreutils 8.0 or later.

Fixing this test will require changes to the opendir/readdir API.

as root. This is important especially when LoopbackFileSystem
is used in combination with AutoUnionFs and the root one of
the overlays is a symlink - in that case we don't want to
link out of the overlay directory structure.

Allows autoconfiguration of symlinked directories

the root path.