v3branch: colour upstream branches

> Otherwise when using 'git branch -vv' it's hard to see them among so
> much output.
>
> Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
> ---
>
> This time with strbuf.
>
>  Documentation/config.txt |  3 ++-
>  builtin/branch.c         | 38 ++++++++++++++++++++++++++++++--------
>  2 files changed, 32 insertions(+), 9 deletions(-)
>
> diff --git a/Documentation/config.txt b/Documentation/config.txt
> index bc750d5..302533f 100644
> --- a/Documentation/config.txt
> +++ b/Documentation/config.txt
> @@ -794,7 +794,8 @@ color.branch::
>  color.branch.<slot>::
>  	Use customized color for branch coloration. `<slot>` is one of
>  	`current` (the current branch), `local` (a local branch),
> -	`remote` (a remote-tracking branch in refs/remotes/), `plain` (other
> +	`remote` (a remote-tracking branch in refs/remotes/),
> +	`upstream` (upstream tracking branch), `plain` (other
>  	refs).
>  +
>  The value for these configuration variables is a list of colors (at most
> diff --git a/builtin/branch.c b/builtin/branch.c
> index 00d17d2..26e9322 100644
> --- a/builtin/branch.c
> +++ b/builtin/branch.c
> @@ -40,13 +40,15 @@ static char branch_colors[][COLOR_MAXLEN] = {
>  	GIT_COLOR_RED,		/* REMOTE */
>  	GIT_COLOR_NORMAL,	/* LOCAL */
>  	GIT_COLOR_GREEN,	/* CURRENT */
> +	GIT_COLOR_BLUE,		/* UPSTREAM */
>  };
>  enum color_branch {
>  	BRANCH_COLOR_RESET = 0,
>  	BRANCH_COLOR_PLAIN = 1,
>  	BRANCH_COLOR_REMOTE = 2,
>  	BRANCH_COLOR_LOCAL = 3,
> -	BRANCH_COLOR_CURRENT = 4
> +	BRANCH_COLOR_CURRENT = 4,
> +	BRANCH_COLOR_UPSTREAM = 5,
>  };

> @@ -417,36 +421,54 @@ static void fill_tracking_info(struct strbuf *stat, const char *branch_name,
>  	int ours, theirs;
>  	char *ref = NULL;
>  	struct branch *branch = branch_get(branch_name);
> +	struct strbuf fancy;
> +
> +	strbuf_init(&fancy, 0);
>  
>  	if (!stat_tracking_info(branch, &ours, &theirs)) {
>  		if (branch && branch->merge && branch->merge[0]->dst &&
> -		    show_upstream_ref)
> -			strbuf_addf(stat, "[%s] ",
> -			    shorten_unambiguous_ref(branch->merge[0]->dst, 0));
> +		    show_upstream_ref) {
> +			ref = shorten_unambiguous_ref(branch->merge[0]->dst, 0);
> +			if (want_color(branch_use_color))
> +				strbuf_addf(stat, "[%s%s%s] ",
> +						branch_get_color(BRANCH_COLOR_UPSTREAM),
> +						ref, branch_get_color(BRANCH_COLOR_RESET));
> +			else
> +				strbuf_addf(stat, "[%s] ", ref);
> +		}
>  		return;
>  	}
>  
> -	if (show_upstream_ref)
> +	if (show_upstream_ref) {
>  		ref = shorten_unambiguous_ref(branch->merge[0]->dst, 0);
> +		if (want_color(branch_use_color))
> +			strbuf_addf(&fancy, "%s%s%s",
> +					branch_get_color(BRANCH_COLOR_UPSTREAM),
> +					ref, branch_get_color(BRANCH_COLOR_RESET));
> +		else
> +			strbuf_addstr(&fancy, ref);
> +	}
> +
>  	if (!ours) {
>  		if (ref)
> -			strbuf_addf(stat, _("[%s: behind %d]"), ref, theirs);
> +			strbuf_addf(stat, _("[%s: behind %d]"), fancy.buf, theirs);
>  		else
>  			strbuf_addf(stat, _("[behind %d]"), theirs);
>  
>  	} else if (!theirs) {
>  		if (ref)
> -			strbuf_addf(stat, _("[%s: ahead %d]"), ref, ours);
> +			strbuf_addf(stat, _("[%s: ahead %d]"), fancy.buf, ours);
>  		else
>  			strbuf_addf(stat, _("[ahead %d]"), ours);
>  	} else {
>  		if (ref)
>  			strbuf_addf(stat, _("[%s: ahead %d, behind %d]"),
> -				    ref, ours, theirs);
> +				    fancy.buf, ours, theirs);
>  		else
>  			strbuf_addf(stat, _("[ahead %d, behind %d]"),
>  				    ours, theirs);
>  	}
> +	strbuf_release(&fancy);
>  	strbuf_addch(stat, ' ');
>  	free(ref);
>  }

> @@ -417,36 +421,54 @@ static void fill_tracking_info(struct strbuf *stat, const char *branch_name,
>         int ours, theirs;
>         char *ref = NULL;
>         struct branch *branch = branch_get(branch_name);
> +       struct strbuf fancy;
> +
> +       strbuf_init(&fancy, 0);