config: rename `dummy` parameter to `cb` in git_default_config()

This is the convention elsewhere (and prepares for the case where we may
need to pass callback data).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/config.c b/config.c
index 4051e38..3687c67 100644
--- a/config.c
+++ b/config.c
@@ -1448,13 +1448,13 @@ static int git_default_mailmap_config(const char *var, const char *value)
 	return 0;
 }
 
-int git_default_config(const char *var, const char *value, void *dummy)
+int git_default_config(const char *var, const char *value, void *cb)
 {
 	if (starts_with(var, "core."))
 		return git_default_core_config(var, value);
 
 	if (starts_with(var, "user."))
-		return git_ident_config(var, value, dummy);
+		return git_ident_config(var, value, cb);
 
 	if (starts_with(var, "i18n."))
 		return git_default_i18n_config(var, value);