Fixes several issues in chunker layout
- Fixes a persisting issue from !98 (merged) createBreakToken would not return the correct break token if not all content of the last element with data-ref have been rendered.
- Fixes findOverflow who could not determine whether a node was displayed on the next column with page margin at 0 due to a wrong comparison with floored left position and rounded end position. Now both are rounded.
- Enhancement: findOverflow will skip children more frequently if right and end positions are equals.