read-tree: fix eye-candy.

Anton Blanchard spotted that watching checkout stage of a clone
on a slow terminal takes ages because it forgot to clear the
"once a second happened" flag, so instead of updates the
percentage output for every file it checks out after the first
second has passed.
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
Signed-off-by: NJunio C Hamano <junkio@cox.net>

builtin-read-tree.c

@@ -376,6 +376,7 @@ static void check_updates(struct cache_entry **src, int nr)
 					fprintf(stderr, "%4u%% (%u/%u) done\r",
 						percent, cnt, total);
 					last_percent = percent;
+					progress_update = 0;
 				}
 			}
 		}