ure of the discrimination charged." Hunter v. Allis-Chalmers Corp., Engine Div., 797 F.2d 1417, 1424 (7th Cir. 1986), abrogated on other grounds by Patterson v. McLean Credit Union, 491 U.S. 164, 109 S. Ct. 2363, 105 L. Ed. 2d 132 (1989). And "[h]ostile environment claims are different in kind from discrete acts." Nat'l R.R. P