Resolving git subtree confusion

FYI, there used to be two different git features called subtree which caused a lot of confusion: the official git subtree merging strategy and a third-party open source git subtree script.

As of git version 1.7.11 (July 2012), the script has been merged into the official mainline git (as an optional contrib).

There are also the stree and subrepo projects that are worth considering.