The .. threading macro analyzes as a macro, not interop (jolt-c2l1 tail)

(.. x m ...) failed: the analyzer classified the .. head as a .method interop
call (method-head? matched any "."-prefixed name) and form-special?
(hc-interop-head?) also flagged it, so it never reached the macro check. Exclude
".." from both (the char after "." being "." means the threading macro, not
.method). Corpus 2690->2691. Re-minted.

host/chez/host-contract.ss

@@ -118,6 +118,7 @@
 (define (hc-interop-head? name)
   (let ((n (string-length name)))
     (and (> n 1)
+         (not (string=? name ".."))   ; the .. threading macro, not an interop form
          (or (char=? (string-ref name 0) #\.)
              (char=? (string-ref name (- n 1)) #\.)))))
 (define (hc-special? name)