Support HTTP basic and digest authentication

Support HTTP basic and digest authentication

Natively support the HTTP basic and digest authentication methods
by setting the Authorization header without going through the JREs
java.net.Authenticator API.  The Authenticator API is difficult to
work with in a multi-threaded server environment, where its using
a singleton for the entire JVM.  Instead compute the Authorization
header from the URIish user and pass, if available.

Change-Id: Ibf83fea57cfb17964020d6aeb3363982be944f87
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>