8066258: Re-examine com.sun.nio.file to see if it should be a supported API

[Alan Bateman]

The last remaining JDK-specific API in java.base is the com.sun.nio.file 
API. This needs to be moved to a JDK-specific module, which one is TDB. 
For now I'd like to at least get the refactoring done and move this API 
to jdk.unsupported on a temporary basis. Once the refactoring is in JDK 
9 then it will be trivial to move it. The proposed changes are here:
    http://cr.openjdk.java.net/~alanb/8066258/webrev/

Thanks,
-Alan