rebase: add rebase.updateRefs config option

The previous change added the --update-refs command-line option.  For
users who always want this mode, create the rebase.updateRefs config
option which behaves the same way as rebase.autoSquash does with the
--autosquash option.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/rebase.c

@@ -802,6 +802,11 @@ static int rebase_config(const char *var, const char *value, void *data)
 		return 0;
 	}
 
+	if (!strcmp(var, "rebase.updaterefs")) {
+		opts->update_refs = git_config_bool(var, value);
+		return 0;
+	}
+
 	if (!strcmp(var, "rebase.reschedulefailedexec")) {
 		opts->reschedule_failed_exec = git_config_bool(var, value);
 		return 0;