Issue1442

Mercurial contains the code below for Posix platforms. None of the os.W*
attributes are present in Jython.

def explain_exit(code):
   """return a 2-tuple (desc, code) describing a process's status"""
   if os.WIFEXITED(code):
       val = os.WEXITSTATUS(code)
       return _("exited with status %d") % val, val
   elif os.WIFSIGNALED(code):
       val = os.WTERMSIG(code)
       return _("killed by signal %d") % val, val
   elif os.WIFSTOPPED(code):
       val = os.WSTOPSIG(code)
       return _("stopped by signal %d") % val, val
   raise ValueError(_("invalid exit code"))

Frank Wierzbicki says: "I would say that (for now) acting like being on
Jython has the same disadvantages as being on Windows is the right
approach, after all, it could be on Windows, and it is inconvenient to
check for Windows from Jython." This seems sensible to me, so a "wont
fix"/"rejected" resolution would be fine if this is not reasonable for
Jython.

For future reference in case of a "wont fix"/"rejected", the workaround
that Mercurial uses on Windows is:

def explain_exit(code):
   return _("exited with status %d") % code, code

We should see if JNR has support for these codes.

Corresponding constants to the functions are available in JNR Constants, https://github.com/jnr/jnr-constants/blob/master/src/main/java/jnr/constants/platform/WaitFlags.java, so it is possible to readily support