The xcurl_off_t() helper function is used to cast size_t to
curl_off_t, but some compilers gave warnings against the code to
ensure the casting is done without wraparound, when size_t is
narrower than curl_off_t. This warning has been squelched.
* tb/xcurl-off-t:
remote-curl.c: xcurl_off_t is not portable (on 32 bit platfoms)