8196787: (ch) Moving network channels to use j.u.c locks

[Alan Bateman]

I have a number of patches in the works that re-work some of the locking 
in the NIO networking channels and also split the blocking and 
non-blocking code paths. Part of the motivation is the 
complexity/overhead dealing with async close and interrupt of blocking 
operations, another part is preliminary work to prepare the 
implementations for fibers.

To get started, I'd like to replace the read/write locks used in the 
networking channels to use j.u.c. locks. The changes are easy to review:
    http://cr.openjdk.java.net/~alanb/8196787/webrev/

There are a few small clean-ups in the patch, this is mostly to keep as 
much noise out of the follow-up changes. The dropping of the ready 
parameter from the native checkConnect is clean-up as the readyToConnect 
flag (dates from 1.4) isn't always reliable to use.

-Alan