Downgrade "Failed to hand off onionskin" messages

They're typically redundant with the "Your computer is too slow"
messages. Fixes bug 7038; bugfix on 0.2.2.16-alpha.

(In retrospect, we should have fixed this bug back in ticket 1042.)

changes/bug7038

@@ -0,0 +1,5 @@
+  o Minor bugfixes (log messages):
+    - Downgrade "Failed to hand off onionskin" messages to "debug"
+      severity, since they're typically redundant with the "Your computer
+      is too slow" messages. Fixes bug 7038; bugfix on 0.2.2.16-alpha.
+

src/or/command.c

@@ -420,14 +420,7 @@ command_process_create_cell(cell_t *cell, or_connection_t *conn)
 
     /* hand it off to the cpuworkers, and then return. */
     if (assign_onionskin_to_cpuworker(NULL, circ, onionskin) < 0) {
-#define WARN_HANDOFF_FAILURE_INTERVAL (6*60*60)
-      static ratelim_t handoff_warning =
-        RATELIM_INIT(WARN_HANDOFF_FAILURE_INTERVAL);
-      char *m;
-      if ((m = rate_limit_log(&handoff_warning, approx_time()))) {
-        log_warn(LD_GENERAL,"Failed to hand off onionskin. Closing.%s",m);
-        tor_free(m);
-      }
+      log_debug(LD_GENERAL,"Failed to hand off onionskin. Closing.");
       circuit_mark_for_close(TO_CIRCUIT(circ), END_CIRC_REASON_RESOURCELIMIT);
       return;
     }