[8u] approval request for 8148379: jdk.nashorn.api.scripting spec. adjustments, clarifications

[Sundararajan Athijegannathan]

Please approve the following backport:

bug: https://bugs.openjdk.java.net/browse/JDK-8148379
jdk9 review thread: 
http://mail.openjdk.java.net/pipermail/nashorn-dev/2016-February/005973.html
jdk8u webrev: http://cr.openjdk.java.net/~sundar/8148379/8u/webrev.00/

the patch wouldn't apply 'as is' (apart from source layout changes). I 
had to do manual merge in two files:

build.xml:

http://cr.openjdk.java.net/~sundar/8148379/8u/webrev.00/make/build.xml.udiff.html

-- because jdk8u build.xml and jdk9-dev build.xml are different now and 
hence line numbers don't match

http://cr.openjdk.java.net/~sundar/8148379/8u/webrev.00/src/jdk/nashorn/api/scripting/AbstractJSObject.java.udiff.html

-- 8u source is slightly different.

I'm cc'ing nashorn-dev alias as well.

-Sundar