master: fix the exit value of subprocesses

The wait() system call isn't the exit value of the process.

From the perldoc :

    This is just the 16-bit status word returned by the traditional Unix wait()
    system call (or else is made up to look like it). Thus, the exit value of
    the subprocess is really ($?>> 8 ), and $? & 127 gives which signal, if
    any, the process died from, and $? & 128 reports whether there was a core
    dump.