[vector] Add back Vector.div with tests

[Paul Sandoz]

Hi,

  http://cr.openjdk.java.net/~psandoz/panama/vector-div-integral/webrev/ <http://cr.openjdk.java.net/~psandoz/panama/vector-div-integral/webrev/>

This adds back Vector.div with support for int etc, and fixes a few issues ensuring an an ArithmeticException is thrown. 

Tests are also added, with a trick to replace a 0 denominator value with 1, plus some additional simple tests, checking that an ArithmeticException is thrown for div by 0.

Paul.