Fix bad interaction between NOTIFY processing and V3 extended query

protocol, per report from Igor Shevchenko.  NOTIFY thought it could
do its thing if transaction blockState is TBLOCK_DEFAULT, but in
reality it had better check the low-level transaction state is
TRANS_DEFAULT as well.  Formerly it was not possible to wait for the
client in a state where the first is true and the second is not ...
but now we can have such a state.  Minor cleanup in StartTransaction()
as well.