nicer display of thin pack completion

In the same spirit of prettifying Git's output display for mere mortals,
here's a simple extension to the progress API allowing for a final
message to be provided when terminating a progress line, and use it for
the display of the number of objects needed to complete a thin pack,
saving yet one more line of screen display.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

progress.h

@@ -9,5 +9,6 @@ struct progress *start_progress(const char *title, unsigned total);
 struct progress *start_progress_delay(const char *title, unsigned total,
 				       unsigned percent_treshold, unsigned delay);
 void stop_progress(struct progress **progress);
+void stop_progress_msg(struct progress **progress, const char *msg);
 
 #endif