Suggested fix for JDK-4724038 (Add unmap method to MappedByteBuffer)

[Mike Hearn]

Sorry, seems I must have hit send without noticing.

Windows has this:

https://msdn.microsoft.com/en-us/library/windows/desktop/aa366890(v=vs.85).aspx

However the question is, what happens if you remap a range and then unmap
the file from that same range?

I'm assuming the file unmap operation deletes the mappings entirely.