RFR: 8153334: Replace BufferedInputStreams use of AtomicReferenceFieldUpdater with Unsafe

[Claes Redestad]

Hi,

BufferedInputStream is loaded early, and uses 
AtomicReferenceFieldUpdater to provide
CAS functionality to allow for closing streams asynchronously. Using 
Unsafe directly instead
does the exact same thing in the end, but avoids loading a few (4) 
classes and thus brings
us a small startup improvement.

Bug: https://bugs.openjdk.java.net/browse/JDK-8153334
Webrev: http://cr.openjdk.java.net/~redestad/8153334/webrev.01/

Thanks!

/Claes