I see Sam's latest blog says:
"Yesterday, Radio Sport reported that Fifa had "clarified" the away goals rule in respect to New Zealand's showdown with Bahrain. Apparently, and contrary to previous understanding, away goals will count as a tiebreaker in extra time (the playoff will enter extra time if the match is tied 0-0 at full time, as it did in Manama)."
One part of me says, "phew" because this is how I understood it to work and it saves me having to release a late bugfix to my WC qualifiers spreadsheet.
The other says, "bugger" because it puts the All Whites at a potential disadvantage if we get to extra-time, albeit one partially offset by having the home advantage for extra-time.
Still, at least we now know - FIFA use the same method as the Champions League for extra-time away goals.