Fix iterator collection removal algorithm

It has two bugs, see:
https://www.w3.org/Bugs/Public/show_bug.cgi?id=25430
Also shortened the wording in two places while I was here (use
"inclusive descendant," and skip redundant pointerBeforeReferenceNode
check).
Merge pull request #10 from ayg/iterator-removal-fix

Fix iterator collection removal algorithm
Use group