So `git_buf_attach` will free the previous pointer when it sets the new one - so I wanted to avoid the `git_buf_*` functions entirely to make it really obvious that this was not really a real `git_buf_`...  (I suppose I could have swapped `git_buf`'s around since I don't need to free them, but this seemed cleaner.)  If you're opposed, I can take another wack at it.