need early validation of genesis transactions

INDY-219 showed that we could have an invalid genesis transactions file (in that case, one that used the symbolic identifier "TRUSTEE" instead of its numeric equivalent, 0) and not notice for a while.

I want it to be the case that an invalid genesis transactions file causes an immediate failure with a clear error message that identifies the problematic line. We may have already done this as part of our input validation effort; if not, we need to add additional logic.