DailyRollingFileAppender
1. Rollover on close only when 'MaxBackupIndex' is bigger then zero
2. Rollover on init by check the log file's last modified time
DailyRollingFileAppender
1. Rollover on close only when 'MaxBackupIndex' is bigger then zero
2. Rollover on init by check the log file's last modified time
DailyRollingFileAppender add new property 'MaxBackup'
This property limits how many backup files are kept for
entire logging period; e.g. how many <tt>log.2009-11-07</tt>,
<tt>log.2009-11-08</tt> etc. files are kept.

If 'MaxBackupIndex' is set for DailyRollingFileAppender,
Rollover with 'MaxBackup' will keep all log files in single period.

For example: MaxBackupIndex=2, MaxBackup=2.
There are log files:
  log --created at 2013-07-17
  log.2013-07-15
  log.2013-07-15.1
  log.2013-07-16
  log.2013-07-16.1
  log.2013-07-16.2

Today is 2013-07-18, then after rollover, files are:
  log --created at 2013-07-18
  log.2013-07-16
  log.2013-07-16.1
  log.2013-07-16.2
  log.2013-07-17