changed the way appenders are loaded, so that they don't need to include log4js as a direct dependency

lib/log4js.js

@@ -213,8 +213,9 @@ function validateCategories(cats) {
 }
 
 function clearAppenders () {
-  debug("clearing appenders");
+  debug("clearing appenders and appender makers");
   appenders = {};
+  appenderMakers = {};
 }
 
 function appenderByName(name) {
@@ -230,7 +231,6 @@ function configureAppenders(appenderMap) {
   Object.keys(appenderMap).forEach(function(appenderName) {
     var appender, appenderConfig = appenderMap[appenderName];
     loadAppender(appenderConfig.type);
-    appenderConfig.makers = appenderMakers;
     try {
       appenders[appenderName] = appenderMakers[appenderConfig.type](
         appenderConfig, 
@@ -247,21 +247,26 @@ function configureAppenders(appenderMap) {
 
 function loadAppender(appender) {
   var appenderModule;
-  try {
-    appenderModule = require('./appenders/' + appender);
-  } catch (e) {
+
+  if (!appenderMakers[appender]) {
+    debug("Loading appender ", appender);
     try {
-      appenderModule = require(appender);
-    } catch (err) {
-      throw new Error("Could not load appender of type '" + appender + "'.");
+      appenderModule = require('./appenders/' + appender);
+    } catch (e) {
+      try {
+        debug("Appender ", appender, " is not a core log4js appender.");
+        appenderModule = require(appender);
+      } catch (err) {
+        throw new Error("Could not load appender of type '" + appender + "'.");
+      }
     }
-  }
-  appenderMakers[appender] = appenderModule.configure.bind(appenderModule);
+    appenderMakers[appender] = appenderModule(layouts, levels);
+  }  
 }
 
 module.exports = {
   getLogger: getLogger,
-  configure: configure,
+  configure: configure
 };
 
 //set ourselves up