Follows #19266, #8553, Close #18553, now there are only three `Run..(&RunOpts{})` functions.
* before: `stdout, err := RunInDir(path)`
* now: `stdout, _, err := RunStdString(&git.RunOpts{Dir:path})`
This PR registers requests with the process manager and manages hierarchy within the processes.
Git repos are then associated with a context, (usually the request's context) - with sub commands using this context as their base context.
Signed-off-by: Andrew Thornton <art27@cantab.net>
