RFR 8199849: HttpServer/BasicAuthenticator: unicode bytes are not correctly handled

[Michael McMahon]

This change went through a couple of rounds of review before, and I got 
diverted to something else
at the time. So, just picking it up now.

Bug: https://bugs.openjdk.java.net/browse/JDK-8199849

Webrev: http://cr.openjdk.java.net/~michaelm/8199849/webrev.3/index.html

CSR: https://bugs.openjdk.java.net/browse/JDK-8215275

The two tests were contributed by Patrick Concannon.

Thanks,
Michael.