Work around HPUX /bin/cc compiler bug.

Work around HPUX /bin/cc compiler bug.

(card_of_complement): Use cleaner `sizeof in_set'
rather than `N_CHARS * sizeof(in_set[0])'.  Using HPUX's /bin/cc
(aC++/ANSI C B3910B A.05.55 [Dec 04 2003]) on an ia64-hp-hpux11.22
system, those two expressions are not the same (256 vs. 1024).
The effect of this problem was that `tr -c x y' would fail:
tr: when not truncating set1, string2 must be non-empty