Chapter 1 Is_unique.cc : function isUniqueChars_noDS runs in O(n^2) instead of O(n logn)

[zaffnet]

As Hint #132 suggests, isUniqueChars_noDS can be implemented in O(n logn) by sorting. Also, inside main(), the function isUniqueChars_noDS is not tested while the function isUniqueChars_bitvector is tested twice.