3087 Addressed review comments

Good deal of commentary clean up, rolled back IOService reference
changes to DNSClient, and most significantly added unit tests
for NameChangeTransaction::sendUpdate.  These tests involve an
actual message exchange.
[3087] Minor corrections for D2 unit tests

Addressed minor compilation issues in nc_trans_unittests.cc under
FreeBSD.
[3087] Additional minor review updates.

Minor corrections based on re-review.
[3087] Minor review corrections.

Fixed a typo and added a bit more diagnostic output to two unit tests.