[mail] allow to specify SMTP's MAIL FROM address to config.sendmails(). Closes #3373620
Also modify testlib.Email so we don't loose this information and may test it.
ifnotrql('CWConstraintType X WHERE X name "RQLUniqueConstraint"',ask_confirm=False):rql('INSERT CWConstraintType X: X name "RQLUniqueConstraint"',ask_confirm=False)