degrade level (back) to INFO and log trace when commited

should be a compromise as users using an error app would have been
confused by the new ERROR message (wasn't there previously)

Author: kares

src/main/java/org/jruby/rack/AbstractRackDispatcher.java

@@ -46,10 +46,10 @@ protected void handleException(
             final RackResponseEnvironment response) throws IOException {
 
         if ( response.isCommitted() ) {
-            context.log(RackLogger.ERROR, "couldn't handle exception "+ e +" : response is committed");
+            context.log(RackLogger.ERROR, "couldn't handle exception (response is committed)", e);
             return;
         }
-        context.log(RackLogger.ERROR, "resetting rack response due to exception:" + e);
+        context.log(RackLogger.INFO, "resetting rack response due exception: " + e);
         response.reset();
 
         afterException(request, e, response);