[transaction] handle ``mode`` default value in Transaction The transaction mode is now explicitly passed at creation time and always read from the Transaction object. Note that there is a slight behavior change. The transaction mode is now set at the creation of the transaction. Changes made to the default value have no longer any effect on existing transaction.

addressbook
basket
blog
book
calendar
comment
company
email
file
folder
i18ncontent
keyword
link
mailinglist
person
tag
timeseries
vcsfile