Add shortcut in refresh_cache_ent() for marked entries.

When a cache entry has been marked as CE_VALID, the user has
promised us that any change in the work tree does not matter.
Just mark the entry as up-to-date, and continue.
Signed-off-by: NMarius Storm-Olsen <marius@trolltech.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

read-cache.c

@@ -893,6 +893,15 @@ static struct cache_entry *refresh_cache_ent(struct index_state *istate,
 	if (ce_uptodate(ce))
 		return ce;
 
+	/*
+	 * CE_VALID means the user promised us that the change to
+	 * the work tree does not matter and told us not to worry.
+	 */
+	if (!ignore_valid && (ce->ce_flags & CE_VALID)) {
+		ce_mark_uptodate(ce);
+		return ce;
+	}
+
 	if (lstat(ce->name, &st) < 0) {
 		if (err)
 			*err = errno;