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20130927 (Friday, 27 September 2013)
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Started `finan.SuggestionsByVoucher`.

This caused a new subtle optimization in :mod:`lino.core.actors`:

    Non-editable actors won't even call 
    :meth:`get_view_permission <lino.core.actions.Action.get_view_permission>` 
    for actions with `readonly=False`.

This optimization is nice, but in fact the problem was even deeper: 
it was caused by the fact that ledger.Movement 
is declared as Sequenced (because it has a seqno field), 
but (since not meant to be user-edited) 
should not be Duplicable nor should it have MoveUp 
and MoveDown buttons.
I removed `Sequenced` from the base classes and 
manually added a seq_no field because Movement needs nothing else 
from Sequenced. Except for the automatic seqno calculation which was 
not necessary for Movement and too expensive (added a counter in 
Registrable.register() instead.


Cool! For the first time Lino 
(:mod:`lino.modlib.finan`) is able to suggest the entries of 
a bank statement using open transactions. (A function which in fact is 
usually not useful in BankStatements but in PaymentOrders and/or 
JournalEntries.