bisect: fix internal diff-tree config loading

When we run our internal diff-tree to show the bisected commit, we call
init_revisions(), then load config, then setup_revisions(). But that
order is wrong: we copy the configured defaults into the rev_info struct
during the init_revisions step, so our config load wasn't actually doing
anything.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

bisect.c

@@ -901,8 +901,8 @@ static void show_diff_tree(struct repository *r,
 	};
 	struct rev_info opt;
 
-	repo_init_revisions(r, &opt, prefix);
 	git_config(git_diff_basic_config, NULL); /* no "diff" UI options */
+	repo_init_revisions(r, &opt, prefix);
 
 	setup_revisions(ARRAY_SIZE(argv) - 1, argv, &opt, NULL);
 	log_tree_commit(&opt, commit);