- reduce recursion level from 20 to 10 and make a symbolic constant for it.
- pull out the guts of saving and restoring the output buffer into functions
  and take care not to overwrite the error message if an error happened.
file_error(struct magic_set *ms, int error, const char *f, ...)
{
	va_list va;
	va_start(va, f);
	file_error_core(ms, error, f, va, 0);
	va_end(va);
}

file_error(struct magic_set *ms, int error, const char *f, ...)
{
	va_list va;
	va_start(va, f);
	file_error_core(ms, error, f, va, 0);
	va_end(va);
}
