Fix a few more clang-generated warnings.

These are benign, I think. clang warns about casting non-pointer-sized
integers to pointers, but the Windows API actually does sometimes
involve values that are either pointers or _small_ integers, so in the
two cases involved I just cast through ULONG_PTR to silence the
warning. And clang insists that the integer whose address I give to
sk_getxdmdata is still uninitialised afterwards, which is just a lie.

x11fwd.c

@@ -934,7 +934,7 @@ int x11_send(struct X11Connection *xconn, char *data, int len)
          * Write a new connection header containing our replacement
          * auth data.
 	 */
-
+        socketdatalen = 0;             /* placate compiler warning */
         socketdata = sk_getxdmdata(xconn->s, &socketdatalen);
         if (socketdata && socketdatalen==6) {
             sprintf(new_peer_addr, "%d.%d.%d.%d", socketdata[0],