Tests:
Deleting when a selection starts at the beginning of a text following a nested block, and extends out of the enclosing block into the following block.
FIXME: Currently broken! See rdar://problem/4099839/.
Expected Results:
Should see a total of five lines in the red box, with the third line inside of a nested red box. First line should be "one". Next line should be "two". Next line should be "cha cha cha", inside of a nested red box. Next line should be "ur". The last line should be "cha cha cha". Insertion point should be blinking at the start of the fourth line ("ur").