This makes the change mentioned in the log message for r10735 (the previous

revision). So what we'll get here is the following:

Dotted + Dotted = Dotted (from the first case)
Dotted + x      = x      (since x refers to a free use of the dotted var)
x      + Dotted = x      (same)

I think this is correct.

collects/typed-scheme/private/free-variance.ss

@@ -42,9 +42,8 @@
   (define (combine-var v w)
     (cond
       [(eq? v w) v]
-      [(or (eq? v Dotted) (eq? w Dotted))
-       Invariant
-       #;(int-err "Cannot combine Dotted w/ not Dotted: ~a ~a" v w)]
+      [(eq? v Dotted) w]
+      [(eq? w Dotted) v]
       [(eq? v Constant) w]
       [(eq? w Constant) v]
       [else Invariant]))