[8u] approval request for 8157680: Callback parameter of any JS builtin implementation should accept any Callable

[Sundararajan Athijegannathan]

Please approve.

Bug: https://bugs.openjdk.java.net/browse/JDK-8157680

jdk9 review thread:
http://mail.openjdk.java.net/pipermail/nashorn-dev/2016-May/006225.html

jdk8u webrev: http://cr.openjdk.java.net/~sundar/8157680/8u/webrev.00/

The patch would not apply "as is" because there are few 8u specific
calls from Bootstrap.java. CC'ing nashorn-dev team for backport review.

Thanks,

-Sundar