inline DiskLoc Record::getPrev(const DiskLoc& myLoc) {
        _accessing();
        if ( _prevOfs != DiskLoc::NullOfs )
            return DiskLoc(myLoc.a(), _prevOfs);
        Extent *e = myExtent(myLoc);
        if ( e->xprev.isNull() )
            return DiskLoc();
        return e->xprev.ext()->lastRecord;
    }

c = db.c;
c.drop();

a = 0;
c.save( { a:a++ } );

big = new Array( 1024*1024 ).toString();
// Save 3 extents of data.                                                                               
while( c.stats().numExtents < 3 ) {
    c.save( { a:a++, b:big } );
}

savedCount = c.count();
assert.gt( savedCount, 2 );

// Remove all but the first and last documents, with the expectation that the first doc is in the        
// first extent and the last in the last extent.  This leaves the middle extent empty.                   
c.remove( { a:{ $gt:0, $lt:a-1 } } );
assert.eq( 2, c.count() );
assert.eq( 2, c.find().sort( { $natural:1 } ).itcount() );
// Check that reverse iteration properly iterates past the empty middle extent.
// Currently it stops at the empty extent (and only sees one document).
assert.eq( 2, c.find().sort( { $natural:-1 } ).itcount() );