Because the industry loves to define by their differences any directors who aren’t straight white men, the easy takeaway from Andrew Haigh‘s exemplary work on the 2011 indie hit “Weekend” (and, later, on HBO’s “Looking”) was that the British filmmaker was talented at crafting gay love stories. With “45 Years,” though, even the most egregious pigeonholers will amend their description of Haigh as talented, period. If anything, this haunting new drama (adapted from a short story by David Constantine) spotlights the filmmaker’s skill not merely as a chronicler of contemporary gay life, but rather as a master of the two-hander:.