Function git_quickfix::wrapper_pick_and_clean

pub fn wrapper_pick_and_clean(
    repo: &Repository, 
    target_branch: &str, 
    onto_branch: &str, 
    force_new_branch: bool
) -> Result<()>

Wraps the three steps below into one, such that any error can be caught and the git stash can be popped before exiting. In many ways this is a poor-person’s try-finally (or context manager in Python). Using Drop led to multiple borrowing errors. Any improvements along those lines are more than welcome.