MEDIUM: sample: Remove types SMP_T_CSTR and SMP_T_CBIN, replace it by SMP_F_CONST...

MEDIUM: sample: Remove types SMP_T_CSTR and SMP_T_CBIN, replace it by SMP_F_CONST flags

The operations applied on types SMP_T_CSTR and SMP_T_STR are the same,
but the check code and the declarations are double, because it must
declare action for SMP_T_C* and SMP_T_*. The declared actions and checks
are the same. this complexify the code. Only the "conv" functions can
change from "C*" to "*"

Now, if a function needs to modify input string, it can call the new
function smp_dup(). This one duplicate data in a trash buffer.