Add some simple Java clients that use the JavaHL authn API.

* tools/examples/ExampleAuthn.java: New.
* tools/examples/ExampleAuthnOld.java: New.
* tools/examples/ExampleAuthnVeryOld.java: New.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1640533 13f79535-47bb-0310-9956-ffa450edef68