__attribute__: add a few missing format attributes

A public function mem_pool_strfmt() takes printf like parameters,
but is not given an attribute as such.  Also a few file-scope static
functions were missing their format attribute.

Add them.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

wt-status.c

@@ -126,6 +126,7 @@ void status_printf(struct wt_status *s, const char *color,
 	va_end(ap);
 }
 
+__attribute__((format (printf, 3, 4)))
 static void status_printf_more(struct wt_status *s, const char *color,
 			       const char *fmt, ...)
 {