NIO based SocketImpl to replace legacy PlainSocketImpl

[Alan Bateman]

Just another update on the effort to replace the legacy PlainSocketImpl. 
The changes in the sandbox are in good shape. I spent a bit of time 
comparing the behavior differences between the old and new 
implementations and I haven't found anything significant so far. Sergey 
Kuksenko has improved the micro benchmarks that exercise the socket APIs 
and we are about the same, or slightly better, which is good.

I've drafted a JEP with all the details here:
    http://openjdk.java.net/jeps/8218559

We will need help to test it. The Socket/ServerSocket APIs date from JDK 
1.0 so it's likely there is a lot of dusty code using them. At the same 
time, newer libraries and servers have moved on to to the NIO APIs or 
something else. So if you have code using Socket/ServerSocket and have 
cycles to try it the changes in the sandbox then it would be very useful.

-Alan