[8u20] Request for approval : 8031737 CHECK_NULL and CHECK_EXCEPTION macros cleanup

[Phil Race]

This is a backport to JDK 8 of a JDk 9 fix which provides some handy JNI 
util macros :-

Review thread (picking up at the point the 8 review starts) :
http://mail.openjdk.java.net/pipermail/core-libs-dev/2014-February/025049.html
JDK8 webrev : http://cr.openjdk.java.net/~prr/8031737.8u

This backport is a necessary precursor to backporting other fixes that
reference the macros.

-phil.