JDK jar/zip code should use unsigned library support

The changes for 4504839: "Java libraries should provide support for unsigned integer arithmetic" added library support for unsigned operations. The jar/zip code uses some of those operations and should be updated to take advantage of the new library methods.

See core-libs-dev thread:
http://mail.openjdk.java.net/pipermail/core-libs-dev/2012-January/009046.html
See
http://hg.openjdk.java.net/jdk8/tl/jdk/rev/946056e6116e