[PATCH 0 of 3] git subrepos

[Eric Eisner]

Here's my experimental git subrepo implementation.

It includes a test for the standard dvcs use case of pull,merge,commit,push, all on a git branch without breaking anything.

Although the svn subrepo implementation verbosely prints all svn output, some git commands have the annoying habit of printing to stderr in case of success, so I ignore most output for simplicity. I think it would be useful to show progress information when cloning or pushing etc, but that's for a further effort.