[8u66] Request for Approval: 8130234: Get rid of JSType.isNegativeZero

[Attila Szegedi]

Please approve.

Bug: https://bugs.openjdk.java.net/browse/JDK-8130234
jdk9 webrev: http://cr.openjdk.java.net/~attila/8130234/webrev.jdk9
jdk9 review thread: http://mail.openjdk.java.net/pipermail/nashorn-dev/2015-July/004846.html

Changes apply cleanly to jdk8u-dev after path reshuffling from modular source code layout.

Thanks,
  Attila.