Ends the current transaction by writing all inserts, updates and deletes
to the disk and unlocking all row and table locks held by the transaction.
This command is only needed if autocommit is set to false.
A FrontBase link identifier
returned by fbsql_connect() or
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
TRUE on success or
FALSE on failure.