evolve: add logic to handle a particular case in divergence resolution Case is: In content divergence, to check if the two csets are on different parent or same parent what we do is find gca of the two csets and then compare it with the singlesuccessors of two csets's parents. Now, if gca is same as singlesuccessors of both the csets then we conclude that both are on the same parent which is not totally correct as it is possible that both the parents of two csets are obsolete with a single successor. This patch adds the logic to cover the above metioned case correctly, deciding the part when we need to relocate a cset to other side while resolving the stack of divergent csets. Changes in test file demonstrate that before this patch we were not doing it right because it should have relocated every node to other side instead of just relocating the first one from the stack.

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