Warn unconditionally, give context on verbose=t
Needed generalized txn generater for split reverts.

Bin specialized normal and multi-currency function in favour of
generic one.
Multi-currency txn sometimes needs account 'type'

Optional 4th argument per txn split is account 'type' - used to
disambiguate pure currency trading accounts from std ones.
Add thoughts on PayPal reverts to TODO.
Fix local var name.

The name split was ambiguous - there's the gnc xml namespace with
the exact same label.
Mention delete_txn.py in TODO.
Cleanup TODO - revert, refund, currency transfer is done now.