Problem - In the event that the master is extended with a new checksum algorithm not
       	  known to the slave, the slave will deduce that there is no checksum support
       	  in the master. However, the master will send events with the new checksum
       	  while the slave treats it as no checksum, with potential for treating the
       	  checksum as part of the event body.

Fix - Added a new variable BINLOG_CHECKSUM_ALG_UNKNOWN to denote the checksum algorithm
      used by master, which is unknown to the slave.

      Changed the code that checks the result of the 
  
        SET @master_binlog_checksum = @@global.binlog_checksum  
  
      on the slave.
       
      Set mi->checksum_alg_before_fd to BINLOG_CHECKSUM_ALG_OFF if an error is reported while
      executing the query.
             
      Incase there is no error and the checksum algorithm is unknown function find_type 
      returns 0 and the value of mi->checksum_alg_before_fd == -1. 
      In such a case we stop the slave with an error message.