revisions API: have release_revisions() release "commits"

Extend the the release_revisions() function so that it frees the
"commits" in the "struct rev_info".

We don't expect to use this "struct rev_info" again, so there's no
reason to NULL out revs->commits, as e.g. simplify_merges() and
create_boundary_commit_list() do.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

revision.c

@@ -2928,6 +2928,7 @@ int setup_revisions(int argc, const char **argv, struct rev_info *revs, struct s
 
 void release_revisions(struct rev_info *revs)
 {
+	free_commit_list(revs->commits);
 	object_array_clear(&revs->pending);
 }