RFR: 8280881: (fs) UnixNativeDispatcher.close0 may throw UnixException

[Brian Burkhalter]

Re-specify `sun.nio.fs.UnixNativeDispatcher.close0()` to throw `sun.nio.fs.UnixException` and modify callers either to ignore it or to rethrow it as an `IOException`, as appropriate.

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Commit messages:
 - 8280881: (fs) UnixNativeDispatcher.close0 may throw UnixException

Changes: https://git.openjdk.java.net/jdk/pull/7467/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7467&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8280881
  Stats: 112 lines in 8 files changed: 78 ins; 0 del; 34 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7467.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7467/head:pull/7467

PR: https://git.openjdk.java.net/jdk/pull/7467