(Property Interface consolidation) Removed a redundancy in interface

(Property Interface consolidation)  Removed a redundancy in interface
definitions:

from here (for several of the interfaces):

    public interface KeepWithNext {
        public interface WithinPage extends GenericKeep.Enums.WithinPage { }
        public interface WithinLine extends GenericKeep.Enums.WithinLine { }
        public interface WithinColumn extends GenericKeep.Enums.WithinColumn { } }

to here:

    public interface KeepWithNext extends GenericKeep.Enums { }

git-svn-id: https://svn.apache.org/repos/asf/xmlgraphics/fop/trunk@197211 13f79535-47bb-0310-9956-ffa450edef68