Compare two M-texts using the current locale.
function compares the two M-texts
It returns an integer less than, equal to, or greater than zero if
is found, respectively, to be less than, to match, or to be greater than
The comparison is based on texts as appropriate for the current locale (LC_COLLATE).
This function makes use of information that is automatically cached in the M-texts as a text property. So, the second call of this function with
finishes faster than the first call.