title: git log history of all branch merges
body: <p>I would like to find a way to identify all merges to a branch. I can see the results I want but when the branch that the merge was from changes the merge from is missing in the merge to. Ideally I would like to see a history of this. For example I have release branch1 and I merge in fix1. I can see this with git branch --merged but when fix1 branch changes the command git branch --merged does not list fix1 again because the head has moved. How can I see this data historically?</p>