Use SIZE_T_MAX instead of ulong as a limit for key_buffer_size to allow key_bufer_size > 4G on Windows in 5.1. This is for bug #5731.


include/my_global.h:
  Added SIZE_T_MAX.
sql/mysqld.cc:
  Use SIZE_T_MAX instead of ulong as a limit for key_buffer_size to allow key_bufer_size > 4G on Windows in 5.1.