RFR: JDK-8064736: Part of java.util.jar.JarFile spec looks confusing with references to Zip

[Xueming Shen]

Hi

Please help review

issue: https://bugs.openjdk.java.net/browse/JDK-8064736
webrev: http://cr.openjdk.java.net/~sherman/8064736

The goal is to have the api doc for these two methods to be
consistent with the rest of the apis, especially the ISE exception part.

Thanks!
-Sherman