string-width for long strings

[poeck@informatik.uni-wuerzburg.de (Karsten Poeck)]

String-width seems to be restricted to strings smaller than 255 chars
(since it calls with-pstrs ?).
Is there an other way to implement long-string-width than to repeatedly
call string-width with subseqs of the long string shorter that 255 and too
add the results?

Karsten