MinGW make type warning in unit-test-server.c (closes #180)

Thanks to Marjan Tomas

tests/unit-test-server.c

@@ -202,7 +202,7 @@ int main(int argc, char*argv[])
                 for (i=0; i < req_length; i++) {
                     printf("(%.2X)", req[i]);
                     usleep(500);
-                    send(w_s, req + i, 1, MSG_NOSIGNAL);
+                    send(w_s, (const char*)(req + i), 1, MSG_NOSIGNAL);
                 }
                 continue;
             }