mismatch in send/receive sizes of int32/int64

I think the root cause for #505 (closed) could be how ints are being sent/received. For example, an int32_t is sent with a LABEL tag and is 4 bytes. But a LABEL is received in UIPstream as a label and could be 32 or 64-bits (depending on WM_LABEL_SIZE). It would seem to be the same for int64, but we probably haven't been sending those about too much in that form.