added optional support for collecting IDFV

Not for merge.  Just for review.  There's documentation here and there I should upgrade as well.  Mainly, I get a compile error in TATapestryClient.m, which has not been touched in this branch.  I think I might need to upgrade my XCode (current version 4.5.1).  However, upgrading to the latest requires I be on 10.8.  I'll do the upgrades this weekend, but if someone already has a version of XCode that works with this, they can make a quick sanity check.