Commands like Get, Init, Update can't retrieve live out/err?

[tony]

In git, initial checkout and pulls, these are often "buffered". That information is valuable in my case (www.github.com/tony/vcsync) because I want to forward the progress of the update to stdout. Ideally, a couple of repos at a time.

At the present time, Get, Init and Update is hard-coded to use CombinedOutput, which runs the command and waits for completion. This lends me no ability run the command and observe the live output of a git pull, and due to the command and error handling for the (Get/Init/Update) on the repo being tightly-coupled, I can't trivially compose a command for my case without duplicating 90% of the code.

I'm going to present a PR for this for your opinion.

[mattfarina]

@tony I look forward to your PR.