include account name in debug output
fix account selection with hledger

We increase the register output width so we are likely to get the full
unelided account names, up to 80 characters or so. This means we now
require hledger 0.20+.
hledger: if we find many accounts, use the last
tweak --hledger help message
make ledger behave like hledger for ambiguous payees (return last
account); fix test