largefiles: rewrite merge code using dictionary with entry per file In overridecalculateupdates(), we currently only deal with conflicts that result in a 'g' action for either the largefile or a standin. We will soon want to deal cases with 'cd' and 'dc' actions here. It will be easier to reason about such cases if we rewrite it using a dict from filename to action. A side-effect of this change is that the output can only have one action per file (which should be a good change). Before this change, when one of the tests in test-issue3084 received this input (the 'a' in the input was a result of 'cd' conflict resolved in favor of the modified file): 'g': [('.hglf/f', ('',), 'remote created')], 'a': [('f', None, 'prompt keep')], and the user chose to keep the local largefile, it produced this output: 'g': [('.hglf/f', ('',), 'remote created')], 'r': [('f', None, 'replaced by standin')], 'a': [('f', None, 'prompt keep')], Although 'a' actions are processed after 'r' actions by recordupdates(), it still worked because 'a' actions have no effect on merges (only on updates). After this change, the output is: 'g': [('.hglf/f', ('',), 'remote created')], 'r': [('f', None, 'replaced by standin')], Similarly, there are several tests in test-largefiles-update that get inputs like: 'a': [('.hglf/large2', None, 'prompt keep')], 'g': [('large2', ('',), 'remote created')], and when the user chooses to keep the local largefile, they produce this output: 'a': [('.hglf/large2', None, 'prompt keep'), ('.hglf/large2', None, 'keep standin')], 'lfmr': [('large2', None, 'forget non-standin largefile')], In this case, it was not a merge but an update, so the 'a' action does have an effect. However, since dirstate.add() is idempotent, it still has no obserable effect. After this change, the output is: 'a': [('.hglf/large2', None, 'keep standin')], 'lfmr': [('large2', None, 'forget non-standin largefile')],