[Virtuoso-users] fix for jena provider in 6.1 release

[Jesse Sightler]

VirtResSetIter.java:filterDrop was:
public ExtendedIterator filterDrop (final Filter f)
    {
return new FilterIterator (null, this);
    }

This created a FilterIterator with a null filter (leading to
nullpointerexceptions in some obscure usage scenarios).

A corrected (imo) version is:
public ExtendedIterator filterDrop (final Filter f)
    {
        Filter notF = new Filter() {
            @Override
            public boolean accept(Object x)
            {
                return !f.accept(x) ;
            }
        } ;
        return new FilterIterator(notF, this) ;
//return new FilterIterator (null, this);
    }

Thanks,
Jess