ON 64 BIT MACHINES

PROBLEM: When sorting index during repair of
         myisam tables, due to improper casting
         of buffer size variables value of myisam_
         sort_buffer_size is not set greater than
         4GB.

SOLUTION: Proper casting of buffer size variable.
          myisam_buffer_size changed to unsigned
          long long to handle size > 4GB on
          linux as well as windows.