Rename resolve_ref() to resolve_ref_unsafe()

resolve_ref() may return a pointer to a shared buffer and can be
overwritten by the next resolve_ref() calls. Callers need to
pay attention, not to keep the pointer when the next call happens.

Rename with "_unsafe" suffix to warn developers (or reviewers) before
introducing new call sites.

This patch is generated using the following command

git grep -l 'resolve_ref(' -- '*.[ch]'|xargs sed -i 's/resolve_ref(/resolve_ref_unsafe(/g'

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/commit.c b/builtin/commit.c
index e36e9ad..4d39d25 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -1304,7 +1304,7 @@
 	rev.diffopt.break_opt = 0;
 	diff_setup_done(&rev.diffopt);
 
-	head = resolve_ref("HEAD", junk_sha1, 0, NULL);
+	head = resolve_ref_unsafe("HEAD", junk_sha1, 0, NULL);
 	printf("[%s%s ",
 		!prefixcmp(head, "refs/heads/") ?
 			head + 11 :