RFR 8156497: Add jar tool support for Multi-release modular JARs

[Mandy Chung]

> On May 23, 2016, at 8:05 AM, Chris Hegarty <chris.hegarty at oracle.com> wrote:
> 
> Updated webrev:
>  http://cr.openjdk.java.net/~chegar/8156497.01/


Looks fine to me.

Minor comment on the test, “9” is hardcoded in a few places.  It might be good to prepare for the future release e.g. use Runtime.version().major() + 1 instead.

e.g.
 257             "-C", mrjarDir.toString(), "META-INF/versions/9/module-info.class”,
 760         Path versionSection = metaInfDir.resolve("versions").resolve("9");

Mandy