* Purpose : get length of a string in user memory
* Params : str - address of string in user memory
* Returns : length of string *including terminator*
* or zero on exception, or n + 1 if too long
*/
* Purpose : get length of a string in user memory
* Params : str - address of string in user memory
* Returns : length of string *including terminator*
* or zero on exception, or n + 1 if too long
*/