By aggressively cutting costs and boosting revenue from medical care, Boston-based Caritas Christi Health Care is on track to post operating income of $31.1 million for the fiscal year ending Sept. 30, compared to a $20.4 million loss last year. The anticipated swing of more than $50 million has been achieved through a series of moves, Caritas officials said. The chain consolidated operations at its six Eastern Massachusetts hospitals, cut jobs and froze salaries, negotiated higher reimbursement rates from insurers, and recruited more specialists to perform more complex and profitable procedures.