myisamchk tool generates warnings when run on an myisam files (.MYI or .MYD)
This is because of the conversion of max_value for certain options in myisamchk 
from singed long to unsigned long

The max value for the options key_buffer_size, read_buffer_size, write_buffer
_size and sort_buffer_size is given as (long) ~0L which becomes -1  when casted
from signed long to longlong and then casted to ulonglong. When (ulonglong) -1 
is compared with maximal value for GET_ULONG data type, we adjust it to 
(ulonglong) ULONG_MAX and throw the warning.

Fixed by using the right max size.

Max values for the variables (from mysqld.cc)
----------------------------
1. key_buffer_size
   5.0: ULONG_MAX
   5.1: SIZE_T_MAX
   6.0: SIZE_T_MAX

2. read_buffer_size and write_buffer_size
   5.0: INT_MAX32
   5.1: INT_MAX32
   6.0: INT_MAX32

3. sort_buffer_size (aka myisam_sort_buffer_size)
   5.0: UINT_MAX32
   5.1: ULONG_MAX
   6.0: ULONG_MAX

Note: testcase not attached