8196956: (ch) More channels cleanup

[Alan Bateman]

This is a further small patch to the network channels in advance of more 
complicated changes to split the blocking/non-blocking code paths. The 
changes in this patch are very simple and amount to:

- AbstractSelectableChannel::isBlocking changed to not block on regLock
- the ServerSocketChannel socket adaptors now consistently checks the 
blocking mode
- fix DatagramChannelImpl constructor to consistency track the the UDP 
socket usage

The webrev is here:
   http://cr.openjdk.java.net/~alanb/8196956/webrev/index.html

(ignore the change to make/autoconf/lib-bundled.m4 in the patch, this is 
to workaround temporary build breakage with build changes pushed to 
jdk/jdk yesterday).

-Alan