PathNodeFs.{addChild,rmChild} now calls Inode.{AddChild,RmChild}
rather than the reverse, and PathNodeFs manages its own locking.

Remove methods:

- FileSystemConnector.renameUpdate
- FileSystemConnector.unlinkUpdate
- FileSystemConnector.createChild
- Inode.CreateChild
- Inode.LockTree

Instead, add File.SetInode(), so Files can update inodes if needed.

This prevents forgetting or overwriting the Ino field.  Add a test.

- LoggingFileSystem
- PathDebugFileSystem
- TimingFileSystem

needed.

all files.

This makes serializing file changes easier, as all removed files will
have explicit deletion entries.