Citations incorrect for suffix array

[Yan-Gu]

In suffix_array.h, the comments are:

// Input must be a sequence of unsigned integer type. Uses a modified
// and optimized version of the algorithm from:
// Apostolico, Iliopoulos, Landau, Schieber, and Vishkin.
// Optimal parallel suffix tree construction.
// STOC '94.
// The work is O(n log n) work in the worst case, but for most inputs
// it does O(n) work beyond a sort on constant length integer keys.
// The depth is O(log^2 n) assuming the sort is within that bound.

It seems that the paper title and conference match, and the author list and bound match, but indeed they are two different papers. It's helpful to fix it.