shell: suppress tracing if verbose < 2

Problem: shell_trace() is called for all pmix server upcalls even
when they are suppressed at the shell.

Since these log entries could be large at scale, avoid the memcpy
overhead by suppressing them locally unless -o verbose=N (N > 1).

Fixes #76

Author: garlick

src/shell/plugins/interthread.c

@@ -35,7 +35,7 @@ struct interthread {
     flux_watcher_t *w;
     struct handler handlers[MAX_HANDLERS];
     int handler_count;
-    bool trace_flag;
+    int verbose;
 };
 
 int interthread_register (struct interthread *it,
@@ -100,7 +100,7 @@ static void interthread_recv (flux_reactor_t *r,
         flux_msg_decref (msg);
         return;
     }
-    if (it->trace_flag) {
+    if (it->verbose > 1) {
         const char *payload;
         if (flux_msg_get_payload (msg, (const void **)&payload, NULL) == 0)
             shell_trace ("pmix server %s %s", topic, payload);
@@ -144,7 +144,7 @@ struct interthread *interthread_create (flux_shell_t *shell)
                                                  it)))
         goto error;
     flux_watcher_start (it->w);
-    it->trace_flag = 1; // temporarily force this on
+    (void)flux_shell_getopt_unpack (shell, "verbose", "i", &it->verbose);
     return it;
 error:
     interthread_destroy (it);