Get or set the user password used with a connection.
link_identifier
A FrontBase link identifier returned by fbsql_connect() or fbsql_pconnect().
If optional and not specified, the function will try to find an open link to the FrontBase server and if no such link is found it will try to create one as if fbsql_connect() was called with no arguments
password
If provided, this will be the new connection password.