Two small cleanups and the offer->ACCOUNT->offer fix

1) When pathfinding, don't output a redundant account node.
This node serves no purpose because expandPath adds the node anyway. It's just a waste of bandwidth and space.

2) Cleanup some stray formatting
Obviously-correct cleanup.

3) Fix offer->ACCOUNT->offer

CAUTION: The third change affects transaction processing and requires planning and coordination in deployment. It should probably be combined with other transaction processing changes. (tefDST_TAG_NEEDED, for example.)
Ah, got it.  So there IS another node after this one that's going to be an order book - you are *about* to add the node, and you're checking whether to _replace_ the old last node, or to add a new node.

This might be clearer if you extracted the repeated code - with proper use of std::move you can do it for free, and it'd be much clearer, like this:

    STPathElement element (
        STPathElement::typeCurrency | STPathElement::typeIssuer,
        xrpAccount(),
        book->getCurrencyOut(),
        book->getIssuerOut());

    auto last = newPath.size() - 1;
    auto isOfferToAccount = last > 1 &&
            newPath[last - 1].isOffer() &&
            newPath[last].isAccount();
    if (isOfferToAccount)
        newPath[last] = std::move (element);
    else
        newPath.push_back (std::move (element));