Use one single std::lock_guard in Run(), and replace the manual
Lock()/Unlock() calls.

Eliminate more unlock/lock transitions, making the code more robust.

Regression from commit 0772e571

Reduces main thread contention.  Avoids blocking the main thread in
"status" commands.

If a directory is a mount point, omit the "directory: " as well.

This bug is years old, but has become more visible now that mount
points are persistent in the state file.