Altering certain grounds for a limited divorce and an absolute divorce; authorizing the court to decree a limited divorce on the ground of irreconcilable differences, if the marriage is irretrievably broken and there is no reasonable expectation of reconciliation; and authorizing the court to decree an absolute divorce on the ground of completion of a 6-month waiting period, if one of the parties has filed for a limited divorce under a certain section of the Act at least 6 months before the filing of the application for divorce.