Added commit graph

[linzhp]

Hi CVSAnalY team,

I decided to put my new changes to CVSAnalY instead of MininGit. This is my first batch of changes. It adds a commit graph to keep track of parents of commits. This commit graph currently only supports Git, as it is not necessary in Subversion and CVS. Hope someone could implement a Bzr version if it is necessary (I am not familiar with Bzr).

With regards to #1, I will pick features that I am actively using from MininGit and merge them into CVSAnalY incrementally, instead of merging all changes at once.

[jgbarah]

Thanks a lot! This is something very much needed. The code seems ok, but I have to have a look at its interactions with the incremental retrieval of information from the git repo. I hope that won't take long time.

[andygrunwald]

@jgbarah any new information here?

[andygrunwald]

@linzhp Can you rebase this PR?
Then i will it give a try to test :)

[linzhp]

Rebased

[andygrunwald]

Hey @linzhp,

thanks for this awesome contribution.
I`ve checked this (with executing it with + without your changes + checking the commit_graph table). It works fine. Thanks :)