[MERGE] Remove manual notification of transaction finishing on versioned files.

[Martin Pool]

None of the occurrences of get_scope have a docstring, and the news entry
is not particularly illuminating either.  There should be something
somewhere.  For instance what is get_scope meant to return, and should it
be passed to the constructor or assigned into the instance.

If we are introducing a new top level concept maybe it should have a
paragraph or three in the glossary of the developer guide.
Like

  A scope controls when an in-memory object is valid.  The scope itself
  is an opaque token, assigned by the caller.