(Reuters) - International Business Machines Corp missed analysts' estimates for third-quarter revenue on Wednesday, overshadowing a profit beat and sending its shares down 3% in extended trading.The Armonk, New York-based technology services giant, which wrapped up the mega cloud merger with Linux maker Red Hat Inc earlier this year, has faced years of revenue declines in the process of shifting focus to the cloud from its traditional business.Total revenue fell 3.9% to $18.03 billion (14.1..