RFR: 8156484: ZipFile retains too much native memory from caching Inflaters

[Martin Buchholz]

Another batch of ZipFile hackery.  I think I finally understand how
weak references and finalizers interact.
We could eliminate the Inflater cache entirely, but this proposal
keeps a one-element Inflater cache.

http://cr.openjdk.java.net/~martin/webrevs/openjdk9/ZipFile-Inflater-cache/
https://bugs.openjdk.java.net/browse/JDK-8156484

- fixes the memory bloat from cached Inflaters
- removes small races in close
- various other minor improvements