(bug 27283) SqlBagOStuff breaks PostgreSQL txns

(bug 27283) SqlBagOStuff breaks PostgreSQL txns

* SqlBagOStuff should not turn off automatic transaction
    control just like that. Keep previous
    connection for PostgreSQL and SQLite

* 94633ff448e9253c5503124df6748be1fc26b8e2 introduced
    rollback on error to restore sanity
    for the connection. Don't do this
    if you are in the middle of INSERT IGNORE
    and we have a savepoint open.

    Making sure query syntax errors don't
    get silenced by our "wonderful" implementation
    of INSERT IGNORE is bug 35572.

Change-Id: I841b03895e1189c47307fefb1516c4c7c4102e25