[8u60] approval request for 8068431: @since and @jdk.Exported are missing in jdk.nashorn.api.scripting classes and package-info.java files

[A. Sundararajan]

Please approve.

Bug: https://bugs.openjdk.java.net/browse/JDK-8068431
jdk9 review thread: 
http://mail.openjdk.java.net/pipermail/nashorn-dev/2015-January/004075.html
jdk8u webrev: http://cr.openjdk.java.net/~sundar/8068431/8u40/

backported "as is" except for modular source layour difference.

Thanks
-Sundar