added methods and config to turn off console.log replacement (issue #34)

lib/log4js.js

@@ -279,6 +279,12 @@ function configureOnceOff(config) {
         try {
             configureAppenders(config.appenders);
             configureLevels(config.levels);
+
+            if (config.doNotReplaceConsole) {
+                restoreConsole();
+            } else {
+                replaceConsole();
+            }
         } catch (e) {
             throw new Error("Problem reading log4js config " + util.inspect(config) + ". Error was \"" + e.message + "\" ("+e.stack+")");
         }
@@ -339,13 +345,22 @@ function replaceConsole(logger) {
             fn.apply(logger, arguments);
         }
     }
-
-    ['log','debug','info','warn','error'].forEach(function (item) {
-        if (console['_preLog4js_log'] === undefined) {
+    if (console['_preLog4js_log'] === undefined) {
+        logger = logger || getLogger("console");
+        ['log','debug','info','warn','error'].forEach(function (item) {
             console['_preLog4js_'+item] = console[item];
-        }
-        console[item] = replaceWith(item === 'log' ? logger.info : logger[item]);
-    });
+            console[item] = replaceWith(item === 'log' ? logger.info : logger[item]);
+        });
+    }
+}
+
+function restoreConsole() {
+    if (console['_preLog4js_log']) {
+        ['log', 'debug', 'info', 'warn', 'error'].forEach(function (item) {
+            console[item] = console['_preLog4js_'+item];
+            delete console['_preLog4js_'+item];
+        });
+    }
 }
 
 function loadAppender(appender) {
@@ -363,6 +378,9 @@ module.exports = {
     clearAppenders: clearAppenders,
     configure: configure,
 
+    replaceConsole: replaceConsole,
+    restoreConsole: restoreConsole,
+
     levels: levels,
     setGlobalLogLevel: setGlobalLogLevel,
 
@@ -379,8 +397,6 @@ module.exports = {
 
 //set ourselves up if we can find a default log4js.json
 configure(findConfiguration());
-//replace console.log, etc with log4js versions
-replaceConsole(getLogger("console"));
 
 //keep the old-style layouts
 ['basicLayout','messagePassThroughLayout','colouredLayout','coloredLayout'].forEach(function(item) {