Updates a fetchmail.
$session_id, $client_id, $params
Parameters (in $params):
server_id (int(11))
type (varchar(255))
source_server (varchar(255))
source_username (varchar(255))
source_password (varchar(64))
source_delete (varchar(255))
destination (varchar(255))
active (varchar(255))
source_read_all (varchar(255))
Output:Returns the number of affected rows.