The number of law firm mergers in the U.S. is on track with last year’s record number of combinations — a pace that isn’t expected to slow down anytime soon.Statistics released this week by Altman Weil MergerLine show that during the first half of this year, there were 48 mergers or acquisitions involving U.S. law firms.That’s exactly how many combinations occurred in the first half of 2015, when the year-end total of 91 combinations was the highest number across the nation over the nine years …