Re: [PATCH v17 1/7] bisect: move argument parsing before state modification.

> If we start bisecting like this:
> 
> $ git bisect start HEAD HEAD~20
> 
> and then we decide that it was not optimum and we want to start again like 
> this:
> 
> $ git bisect start HEAD HEAD~6
> 
> then issuing the latter command might not work as it did before this patch.
>  
> Before this patch the latter command would do a "git checkout $start_head" 
> before the repeated rev=$(git rev-parse -q --verify "$arg^{commit}") to 
> convert arguments into sha1. And after this patch the order is reversed.
> 
> This means that before this patch "HEAD" in the arguments to "git bisect 
> start" would refer to $start_head because the "git checkout $start_head" 
> changes HEAD. After this patch "HEAD" in the arguments to "git bisect start" 
> would refer to the current HEAD.