[math-fun] Modular notation

In an article in the June-July 2007 Monthly, it is stated that for any prime p >= 5, the harmonic number H_(p-1) == 0 (mod p^2) (where == means a triple equals sign). Huh??? I thought? H_n can't be an integer! Must be a typo. Until I noticed more of the same kinds of apparent errors in the rest of the article. For the first case, H_4 = 1 + 1/2 + 1/3 + 1/4 = 25/12. So apparently x == j (mod N) is defined for rational numbers x, and means that the numerator of x (in lowest terms) == j (mod N) in the old-fashioned sense. Is it common notation to apply modulo to rationals? Of so, when did it begin to be used? --Dan