trac#284: Raise a hint on unsupported XCCDF namespace.
trac#284: Raise a hint on unsupported XCCDF namespace.

mpreisler/openscap,redhatrises/openscap,isimluk/openscap,ybznek/openscap,isimluk/openscap,isimluk/openscap,postfix/openscap,postfix/openscap,jan-cerny/openscap,Hexadorsimal/openscap,jan-cerny/openscap,openprivacy/openscap,OpenSCAP/openscap,jan-cerny/openscap,ybznek/openscap,ybznek/openscap,mpreisler/openscap,jan-cerny/openscap,Hexadorsimal/openscap,Hexadorsimal/openscap,openprivacy/openscap,OpenSCAP/openscap,Hexadorsimal/openscap,OpenSCAP/openscap,Hexadorsimal/openscap,redhatrises/openscap,redhatrises/openscap,redhatrises/openscap,postfix/openscap,ybznek/openscap,openprivacy/openscap,openprivacy/openscap,isimluk/openscap,openprivacy/openscap,isimluk/openscap,mpreisler/openscap,redhatrises/openscap,isimluk/openscap,redhatrises/openscap,OpenSCAP/openscap,jan-cerny/openscap,postfix/openscap,mpreisler/openscap,openprivacy/openscap,jan-cerny/openscap,ybznek/openscap,ybznek/openscap,OpenSCAP/openscap,Hexadorsimal/openscap,postfix/openscap,postfix/openscap,mpreisler/openscap,mpreisler/openscap,OpenSCAP/openscap