Detect line endings when wrapping occurs between elements 

Line ending detection was relying on wrapping occurring near or in a block of collapsed whitespace. When wrapping occurs between two elements, both previous and next rectangles may be defined, though the vertical overlap will be absent.

Line ending detection is still not stable when the wrap point doesn't span a cursor position (as happens when the wrap occurs over whitespace). Fixing this issue is not easy, so these tests demonstrate the current bad behaviour so at least it is somewhat documented.

# Demonstrating line detection problem
1. Download https://drive.google.com/file/d/0B1EH5OPb-RrjZWRwR2hnUnR6N2c/edit?usp=sharing
2. Load it up in the editor (e.g., http://ci.kogmbh.com/deploy/WebODF/webodf-ci-b469-g8c98fcb7/wodotexteditor-ci-b469-g8c98fcb7/localeditor.html)
3. Press the down cursor arrow. Note that the caret doesn't move at all, though the left & right arrows do move left and right.