Loose end from timing shakeup: sshrand.c is now a client of

Loose end from timing shakeup: sshrand.c is now a client of
timing.c, and hence takes its own responsibility for calling
noise_regular() at regular intervals. Again, this means it will be
called consistently in _all_ the SSH-speaking tools, not just those
in which I remembered to call it!

[originally from svn r4913]