As GCC "2.96" notes, "`short int' is promoted to `int' when passed

As GCC "2.96" notes, "`short int' is promoted to `int' when passed
through `...'", and therefore "...you should pass `int' not `short int'
to `va_arg'".

GCC "2.96" apparently fails to compile code that passes "short int" to
"va_arg()", and Red Hat Linux 7.0 uses GCC "2.96", so we fix this, as
per Pekka Savola's note.