Add more random-number noise collection calls.

Mostly on the Unix side: there are lots of places the Windows code was
collecting noise that the corresponding Unix/GTK code wasn't bothering
to, such as mouse movements, keystrokes and various network events.
Also, both platforms had forgotten to collect noise when reading data
from a pipe to a local proxy process, even though in that
configuration that's morally equivalent to the network packet timings
that we'd normally be collecting from.

unix/uxplink.c

@@ -958,6 +958,7 @@ int main(int argc, char **argv)
 
             if (backend_connected(backend)) {
 		ret = read(STDIN_FILENO, buf, sizeof(buf));
+                noise_ultralight(ret);
 		if (ret < 0) {
 		    perror("stdin: read");
 		    exit(1);