[RFC] git-split: Split the history of a git repository by subdirectories and ranges

Hello,

I co-maintain the X C Binding (XCB) project with Jamey Sharp.
Previously, several XCB-related projects all existed under the umbrella
of a single monolithic GIT repository with per-project subdirectories.
We have split this repository into individual per-project repositories.

Jamey Sharp and I wrote a script called git-split to accomplish this
repository split. git-split reconstructs the history of a sub-project
previously stored in a subdirectory of a larger repository. It
constructs new commit objects based on the existing tree objects for the
subtree in each commit, and discards commits which do not affect the
history of the sub-project, as well as merges made unnecessary due to
these discarded commits.  When git-split finishes, it will output the
sha1 for the new head commit, suitable for redirection into a file in
.git/refs/heads.  At that point, you can clone the new head, or copy the
repository and prune out undesired heads, tags, and objects.

I have attached git-split for review.  If the GIT community has any
interest in seeing git-split become a part of GIT, we can write up the
necessary documentation and patch.

We would like to acknowledge the work of the gobby team in creating a
collaborative editor which greatly aided the development of git-split.

- Josh Triplett