When doing an interdiff, it is possible that there could be two commits

in the RB.DiffCommitCollection that have the same commitId property.

However, they may have different properties (however unlikely), so we

now serialize commits with their primary keys and use them for lookup in

history entries instead of the commit ID. This was especially prevalent

in test cases where the commit IDs were not actually representative

(i.e., a hash) of the content of the commit.

Ran unit tests.
Ran JS tests.