RFR 8057113: (fs) Path should have a method to test the filename extension

[Brian Burkhalter]

https://bugs.openjdk.java.net/browse/JDK-8057113
http://cr.openjdk.java.net/~bpb/8057113/webrev.00/

As a first cut at this problem, this patch would add a new method hasExtension() to the java.nio.file.Path interface with a default implementation. The implementation is overridden only by UnixPath. ZipPath does not override it but perhaps should.

Regression tests passed on all platforms both with and without the UnixPath changes (in order to verify the default implementation on all platforms).

Obviously a CSR will be in order.

Thanks,

Brian