RFR: 8156807: Pack200 must support v53.0 class files

[Kumar Srinivasan]

Hi,

Alex or someone please review this simple fix, the first part is
simply bumping the class file version number, and some cleanup
of  redundant constants in the native unpacker.

The second part is fixing up the test, which does not read the
process streams correctly and causes a test hang, simplified
the test with time tested utilities.

http://cr.openjdk.java.net/~ksrini/8156807/webrev.00/

Thanks
Kumar

PS: Appreciate a quick turnaround as this is causing intermittent test
failures in our internal CI systems.