Add optional timezoneOffset config for appenders

Example:
    log4js.configure({
        appenders: [{type: 'console', timezoneOffset: -540}],
        replaceConsole: true
    });

The expected value is the equivalent of (new Date).getTimezoneOffset()
In this example, -540 is the value for JST.
This allows machines members of world-wide-spread cluster to all report
log time-stamps using the same timezone (or adapt the timezone to a
local different from the system)

lib/appenders/console.js

@@ -2,10 +2,10 @@
 var layouts = require('../layouts')
 , consoleLog = console.log.bind(console);
 
-function consoleAppender (layout) {
+function consoleAppender (layout, timezoneOffset) {
   layout = layout || layouts.colouredLayout;
   return function(loggingEvent) {
-    consoleLog(layout(loggingEvent));
+    consoleLog(layout(loggingEvent, timezoneOffset));
   };
 }
 
@@ -14,7 +14,7 @@ function configure(config) {
   if (config.layout) {
     layout = layouts.layout(config.layout.type, config.layout);
   }
-  return consoleAppender(layout);
+  return consoleAppender(layout, config.timezoneOffset);
 }
 
 exports.appender = consoleAppender;

lib/appenders/dateFile.js

@@ -20,8 +20,9 @@ process.on('exit', function() {
  * @pattern the format that will be added to the end of filename when rolling,
  *          also used to check when to roll files - defaults to '.yyyy-MM-dd'
  * @layout layout function for log messages - defaults to basicLayout
+ * @timezoneOffset optional timezone offset in minutes - defaults to system local
  */
-function appender(filename, pattern, alwaysIncludePattern, layout) {
+function appender(filename, pattern, alwaysIncludePattern, layout, timezoneOffset) {
   layout = layout || layouts.basicLayout;
 
   var logFile = new streams.DateRollingFileStream(
@@ -32,7 +33,7 @@ function appender(filename, pattern, alwaysIncludePattern, layout) {
   openFiles.push(logFile);
 
   return function(logEvent) {
-    logFile.write(layout(logEvent) + eol, "utf8");
+    logFile.write(layout(logEvent, timezoneOffset) + eol, "utf8");
   };
 
 }
@@ -52,7 +53,7 @@ function configure(config, options) {
     config.filename = path.join(options.cwd, config.filename);
   }
 
-  return appender(config.filename, config.pattern, config.alwaysIncludePattern, layout);
+  return appender(config.filename, config.pattern, config.alwaysIncludePattern, layout, config.timezoneOffset);
 }
 
 function shutdown(cb) {

lib/appenders/file.js

@@ -26,8 +26,10 @@ process.on('exit', function() {
  *   if not provided then logs won't be rotated.
  * @param numBackups - the number of log files to keep after logSize 
  *   has been reached (default 5)
+ * @param compress - flag that controls log file compression
+ * @param timezoneOffset - optional timezone offset in minutes (default system local)
  */
-function fileAppender (file, layout, logSize, numBackups, compress) {
+function fileAppender (file, layout, logSize, numBackups, compress, timezoneOffset) {
   var bytesWritten = 0;
   file = path.normalize(file);
   layout = layout || layouts.basicLayout;
@@ -64,7 +66,7 @@ function fileAppender (file, layout, logSize, numBackups, compress) {
   openFiles.push(logFile);
 
   return function(loggingEvent) {
-    logFile.write(layout(loggingEvent) + eol, "utf8");
+    logFile.write(layout(loggingEvent, timezoneOffset) + eol, "utf8");
   };
 
 }
@@ -79,7 +81,7 @@ function configure(config, options) {
     config.filename = path.join(options.cwd, config.filename);
   }
 
-  return fileAppender(config.filename, layout, config.maxLogSize, config.backups, config.compress);
+  return fileAppender(config.filename, layout, config.maxLogSize, config.backups, config.compress, config.timezoneOffset);
 }
 
 function shutdown(cb) {

lib/appenders/fileSync.js

@@ -127,8 +127,10 @@ RollingFileSync.prototype.write = function(chunk, encoding) {
  *   if not provided then logs won't be rotated.
  * @param numBackups - the number of log files to keep after logSize 
  *   has been reached (default 5)
+ * @param timezoneOffset - optional timezone offset in minutes
+ *   (default system local)
  */
-function fileAppender (file, layout, logSize, numBackups) {
+function fileAppender (file, layout, logSize, numBackups, timezoneOffset) {
   debug("fileSync appender created");
   var bytesWritten = 0;
   file = path.normalize(file);
@@ -166,7 +168,7 @@ function fileAppender (file, layout, logSize, numBackups) {
   var logFile = openTheStream(file, logSize, numBackups);
   
   return function(loggingEvent) {
-    logFile.write(layout(loggingEvent) + eol);
+    logFile.write(layout(loggingEvent, timezoneOffset) + eol);
   };
 }
 
@@ -180,7 +182,7 @@ function configure(config, options) {
     config.filename = path.join(options.cwd, config.filename);
   }
 
-  return fileAppender(config.filename, layout, config.maxLogSize, config.backups);
+  return fileAppender(config.filename, layout, config.maxLogSize, config.backups, config.timezoneOffset);
 }
 
 exports.appender = fileAppender;

lib/appenders/smtp.js

@@ -28,7 +28,7 @@ function smtpAppender(config, layout) {
       var firstEvent = logEventBuffer[0];
       var body = "";
       while (logEventBuffer.length > 0) {
-        body += layout(logEventBuffer.shift()) + "\n";
+        body += layout(logEventBuffer.shift(), config.timezoneOffset) + "\n";
       }
 
       var msg = {