RFR 9: 8138696 : java.lang.ref.Cleaner - an easy to use alternative to finalization

[mark.reinhold at oracle.com]

Looks good -- thanks for the further simplification.

Minor editorial comments, to add what Kim and Chris noted:

  - In many places you write, e.g., "Cleaner" rather than "{@code
    Cleaner}".  For consistency with the rest of the package it'd be
    better in most cases just to write "cleaner" or, if its nature as
    a class is important, write "{@code Cleaner}".  The same goes for
    Cleanable, Thread, ThreadFactory, and all other types.

  - The specification of Cleaner::create() mentions
    "ThreadContextClassLoader", but that's not actually a type anywhere
    in the JDK.  Suggest "{@linkplain
    java.lang.Thread#getContextClassLoader context class loader}.

  - In the same method, it'd be helpful to provide links into the Thread
    class (or wherever) for the concepts of access-control context and
    thread locals.

- Mark