Extend logging of proceedToAfterExecSpinlocks

Ties in with balderdashy/sails#4502 and balderdashy/sails#4400

While @mikermcneil has valid points that we *should* be using async/await, there are times when callbacks are still used and the message/trace inside `errCbArg` would otherwise be lost.

lib/private/Deferred.js

@@ -804,6 +804,10 @@ function proceedToAfterExecSpinlocks (errCbArg, resultCbArg, extraCbArgs, self,
         '```\n'+
         flaverr.getBareTrace(self._omen)+'\n'+
         '```\n'+
+        'And here is errCbArg:\n'+
+        '```\n'+
+        errCbArg+
+        '```\n'+
         '\n'
       ):'')+
       ' [?] For more help, visit https://sailsjs.com/support\n'+