RFR: 6539707: (fc) MappedByteBuffer.force() method throws an IOException in a very simple test [v3]

[Brian Burkhalter]

> This change proposes to increase the number of retries of `FlushViewOfFile` in the Windows native implementation of `MappedByteBuffer.force()`, and to catch any exception thrown by the native `force()` and rethrow an `UncheckedIOException` with cause set to the intercepted exception. A sentence is added to the specification of `MappedByteBuffer.force()` regarding unspecified errors. The test from the issue description is revised to fail if `force()` throws an exception which is not an `UncheckedIOException`, or if it is an `UncheckedIOException` whose message indicates it was thrown by the Windows native implementation of `force()`.

Brian Burkhalter has updated the pull request incrementally with one additional commit since the last revision:

  6539707: MMU.force0() -> throw IOException; MBB.force(int,int) -> specify throws UncheckedIOException

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/2636/files
  - new: https://git.openjdk.java.net/jdk/pull/2636/files/7199392d..e41ac28a

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=2636&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=2636&range=01-02

  Stats: 17 lines in 3 files changed: 10 ins; 0 del; 7 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2636.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2636/head:pull/2636

PR: https://git.openjdk.java.net/jdk/pull/2636