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/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;