RFR: 8068972: Array.splice should follow the ES6 specification

[Hannes Wallnöfer]

Please review:

Webrev: http://cr.openjdk.java.net/~hannesw/8068972/webrev.00/
Bug: https://bugs.openjdk.java.net/browse/JDK-8068972

This updates the implementation of Array.prototype.splice to conform with ES6 when called with a single argument.

Hannes