added updated for FLUSH LOGS and replication
sql/log.cc
    fixed the log rotation bug when the log name did not change after
    FLUSH LOGS


Docs/manual.texi:
  added updated for FLUSH LOGS and replication
sql/log.cc:
  fixed the log rotation bug when the log name did not change after
  FLUSH LOGS
sql/sql_class.h:
  fixed the log rotation bug when the log name did not change after
  FLUSH LOGS