Fixed warnings on AMD64, thanks to Mooie <mooie@cow.se> for the patch.

* plugins.d/askpass-fifo.c (main): Cast value from TEMP_FAILURE_RETRY
                                   to int, the value the inner
                                   function returns.
* plugins.d/mandos-client.c (init_gpgme): - '' -
  (start_mandos_communication): New variable "ssize_t sret"; used to
                                store return value from
                                "gnutls_record_recv".  Also cast value
                                from TEMP_FAILURE_RETRY as above.
* plugins.d/usplash.c (usplash_write): New variable "ssize_t sret";
                                       used to store return value from
                                       "write".