change LINE 73 : case SYS_WAIT
change check_vaild_ptr() in LINE 48 ~ 54
replaced all check_vaild_ptr() function and changed name of function
'get_arg()' to 'get_argument'
changed name of function 'check_vaild_buffer' to 'check_buffer' and
variable in it, local_buffer to b.
replace 'remove_child_process(cp)' in process.c