Do a better job of prompting for an exchange rate only when needed.
If the debit or credit value of a split changes, prompt for an exchange rate.
Don't prompt for an exchange rate in a register that doesn't have a rate cell
(and fix a bug so that it knows that portfolio registers don't have one).
If the transaction has been autofilled and edited start with a nearby rate
from the prices DB.  If it is an existing transaction start with the exchange
rate it already has.

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@22735 57a11ea4-9604-0410-9ed3-97b8803252fd
Do a better job of calculating debit and credit fractions.
Make gnc_split_register_set_cell_fractions agree with
gnc_split_register_get_debcred_entry.
If the account for a split changes recalculate the fractions.

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@22736 57a11ea4-9604-0410-9ed3-97b8803252fd