config: mark unused callback parameters

The callback passed to git_config() must conform to a particular
interface. But most callbacks don't actually look at the extra "void
*data" parameter. Let's mark the unused parameters to make
-Wunused-parameter happy.

Note there's one unusual case here in get_remote_default() where we
actually ignore the "value" parameter. That's because it's only checking
whether the option is found at all, and not parsing its value.

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

pager.c

@@ -38,7 +38,8 @@ static void wait_for_pager_signal(int signo)
 	raise(signo);
 }
 
-static int core_pager_config(const char *var, const char *value, void *data)
+static int core_pager_config(const char *var, const char *value,
+			     void *UNUSED(data))
 {
 	if (!strcmp(var, "core.pager"))
 		return git_config_string(&pager_program, var, value);