persistent-equivalence

This is a persistent data structure for equivalence relations (known in the imperative world as union-find or disjoint set union). It exhibits optimal performance when used in a linear pattern, but degrades when other access patterns are used. The basic idea is as given by Conchon and Filliatre in their 2007 paper, "A persistent union-find data structure." Unlike the implementation given in the paper, this version is safe with multiple threads, but does not optimize for backtracking. Version 0.3 contains some performance improvements for concurrent applications, and removes the repr function, which was poorly defined and had no good uses.