RFR - 8132734: java.util.jar.* changes to support multi-release jar files

[Steve Drach]

Hi,

Please review the new webrev that addresses the issues raised by Sherman and Alan in the last iteration.  In particular:
- fixed the race condition in isMultiRelease() and another one with the variables ‘version’ and ‘configured’
- changed the fragment for JarURLConnection runtime versioning from ‘rtversioned’ to ‘runtime’, and created documentation for it
- used try with resources to open JarFile in all the tests

Issue: https://bugs.openjdk.java.net/browse/JDK-8132734 <https://bugs.openjdk.java.net/browse/JDK-8132734> 
JEP 238: https://bugs.openjdk.java.net/browse/JDK-8047305 <https://bugs.openjdk.java.net/browse/JDK-8047305> 
Webrev: http://cr.openjdk.java.net/~psandoz/multiversion-jar/jar-webrev/ <http://cr.openjdk.java.net/~psandoz/multiversion-jar/jar-webrev/> 

Thanks,
Steve