add missing "format" function attributes

For most of our functions that take printf-like formats, we
use gcc's __attribute__((format)) to get compiler warnings
when the functions are misused. Let's give a few more
functions the same protection.

In most cases, the annotations do not uncover any actual
bugs; the only code change needed is that we passed a size_t
to transfer_debug, which expected an int. Since we expect
the passed-in value to be a relatively small buffer size
(and cast a similar value to int directly below), we can
just cast away the problem.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

advice.h

@@ -19,6 +19,7 @@ extern int advice_detached_head;
 extern int advice_set_upstream_failure;
 
 int git_default_advice_config(const char *var, const char *value);
+__attribute__((format (printf, 1, 2)))
 void advise(const char *advice, ...);
 int error_resolve_conflict(const char *me);
 extern void NORETURN die_resolve_conflict(const char *me);