Support getting commonAncestor for more than 2 nodes.
Fix bug in retrieving blob object in objectstore.
Return data in right dataType in retrieving rawObject.
Add third-party diff3 js implementations.
Add dart wrapper over diff3.js.
Support non-fast-forward merges.
Add util function to get sha for a blob object.
Delay writing of objects, only when merge is successful.
remove debug messages.
Add todo.
Merge pull request #965 from dart-lang/git_merge

Support non-fast-forward merge.