[vector] co-variant overrides

[Paul Sandoz]

Hi,

This patch adds missing co-variant overrides and also includes a test if we add further methods and forgot about the overrides.

  http://cr.openjdk.java.net/~psandoz/panama/covar-overrides/webrev/ <http://cr.openjdk.java.net/~psandoz/panama/covar-overrides/webrev/>

Paul.