Re: [PATCH 20/20] grep API: plug memory leaks by freeing "header_list"

> When the "header_list" struct member was added in [1] it wasn't made
> to free the list using loop added for the adjacent "pattern_list"
> member, see [2] for when we started freeing it.
>
> Let's start doing o by splitting up the loop in free_grep_patterns()
> into a utility function. This makes e.g. this command leak-free when
> run on git.git:

>         ./git -P log -1 --color=always --author=A origin/master
>
> 1. 80235ba79ef ("log --author=me --grep=it" should find intersection,
>    not union, 2010-01-17)
> 2. b48fb5b6a95 (grep: free expressions and patterns when done.,
>    2006-09-27)
>
> Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>