[server/session] add missing rollback when freeing a db connection
When we let go of a cnxset and give it back to the pool, we need to make
sure it's not in the middle of a transaction.
We got bitten by a migration where the connection used by admin's
repo.connect was not rolled back before attempting the migration,
causing a deadlock because it had a lock on a table. This could
potentially also be an issue for e.g. hooks or looping tasks that didn't
explicitly rollback before calling free_cnxset or moving out of a
ensure_cnx_set block.
addressbook
basket
blog
book
calendar
comment
company
email
file
folder
i18ncontent
keyword
link
mailinglist
person
tag
timeseries
vcsfile