RFR: JDK-8151806 - JImage decompress code needs to be revised to be more effective

[Jim Laskey (Oracle)]

https://bugs.openjdk.java.net/browse/JDK-8151806 <https://bugs.openjdk.java.net/browse/JDK-8151806>
http://cr.openjdk.java.net/~jlaskey/8151806/webrev/index.html <http://cr.openjdk.java.net/~jlaskey/8151806/webrev/index.html>

Clean up some sloppy code.