Set the global level via the configuration object passed to

log4js.configure or target `all` in the `levels` object.

lib/log4js.js

@@ -166,6 +166,9 @@ function configureLevels(levels) {
   if (levels) {
     for (var category in levels) {
       if (levels.hasOwnProperty(category)) {
+        if(category === "all") {
+          setGlobalLogLevel(levels[category]);
+        }
         getLogger(category).setLevel(levels[category]);
       }
     }
@@ -173,7 +176,9 @@ function configureLevels(levels) {
 }
 
 function setGlobalLogLevel(level) {
-  Logger.prototype.level = levels.toLevel(level, levels.TRACE);
+  if(level) {
+    Logger.prototype.level = levels.toLevel(level, levels.TRACE);
+  }
 }
 
 /**
@@ -199,6 +204,7 @@ function configureOnceOff(config, options) {
     try {
       configureAppenders(config.appenders, options);
       configureLevels(config.levels);
+      setGlobalLogLevel(config.globalLevel);
       
       if (config.replaceConsole) {
         replaceConsole();