[crac] RFR: Clear JarFileFactory cache on checkpoint

[Anton Kozlov]

Even after an URL object referring to a jar file is closed, the JarFile remains cached and open. This change cleans the cache, so the JarFile becomes reclaimable. The only user of the changed class, sun.net.www.protocol.jar.JarURLConnection, does not assume any state of the cache.

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Commit messages:
 - Clear JarFileFactory cache on checkpoint

Changes: https://git.openjdk.java.net/crac/pull/14/files
 Webrev: https://webrevs.openjdk.java.net/?repo=crac&pr=14&range=00
  Stats: 84 lines in 3 files changed: 83 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/crac/pull/14.diff
  Fetch: git fetch https://git.openjdk.java.net/crac pull/14/head:pull/14

PR: https://git.openjdk.java.net/crac/pull/14