[minor cleanup]: Use different variable for flux_msg_handler_t pointers

[chu11]

I got confused looking at some code in msg_handler.c and reactor.c until I realized w is used for flux_msg_handler_t pointers and also for flux_watcher_t pointers.

Looking back, flux_msg_handler_t was once flux_msg_watcher_t, thus the legacy naming. We could update it.

[garlick]

Works for me. Sorry for my laziness.

[chu11]

It's worth mentioning if struct flux_msg_handler_spec is updated to change w to something else, that'll incur changes in flux sched as well.

[garlick]

The common use case is to statically initialize

static struct flux_msg_handler_spec sim_htab[] = {
    {FLUX_MSGTYPE_EVENT, "sim.start", start_cb, 0, NULL},
    {FLUX_MSGTYPE_REQUEST, "sched.trigger", trigger_cb, 0, NULL},
    {FLUX_MSGTYPE_EVENT, "sched.res.*", sim_res_event_cb, 0, NULL},
    FLUX_MSGHANDLER_TABLE_END,
};

and then pass to addvec/delvec

   if (flux_msg_handler_addvec (ctx->h, sim_htab, (void *)h) < 0) {
        flux_log (ctx->h, LOG_ERR, "flux_msg_handler_addvec: %s", strerror (errno));
        goto done;
    }

so possibly the name of that structure member won't be a problem in sched.

[garlick]

This should be closed when #1277 is merged, since it makes the w member go away.

[chu11]

it makes the w member go away in the handler spec, but I think it's still used as w in a lot of places (function parameters, etc.).

[garlick]

Oh OK, sounds good.