Adds a summary property to the Commit object which returns just the first line of the commit message and makes the message property contain the entire commit message (previously the message property only contained the first line of the commit message).  This breaks backwards compatibility a little in that the message property now contains a different value but previously there was no way to access the entire commit message from the Commit object and this is in keeping with git vocabulary, where message generally refers to the entire commit message.
(cherry picked from commit 9d2962d8306c894d4cca55bab551677b92d96352)

The path parameter allows you to specify a path to constrain queries by.  This changes potentially breaks backwards compatibility for the Repo.commits and Repo.commits_since methods as it moves the positional arguments.
(cherry picked from commit cc8a20e78da4864060bd0c9279633009bc10d871)

When calling commands that accept treeish and path arguments and there is a path with the same name as a treeish git cowardly refuses to pick one and asks for the command to use the unambiguous syntax where '--' seperates the treeish from the paths.  Add '--' to the git commands to indicate that the argument is a treeish and not a path.
(cherry picked from commit a9a57fa93a2b121ab9b17fcd6062b9a9c9740883)

doesn't need to do the same boring replacing I did.
(cherry picked from commit 10c62aa69193a8bc7b46ca24c2ad1d5008489665)

The imported module is called git (as in "import git"), so it's less
confusing to do so than to call everything GitPython.something.

working directory.

A working directory is dirty if it has any uncommitted changes (in the working
directory or in the index). Bare repositories are by nature always clean.