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!

git-svn-id: svn://svn.tartarus.org/sgt/putty@4913 cda61777-01e9-0310-a592-d414129be87e