Make UpdateClocks and input-polling dspwrappers-based too.

Make UpdateClocks and input-polling dspwrappers-based too.

Those things are the only thing called from ElapsedTime() to be different
between Curses and Raw/X, and were not abstracted yet.

The poll-based polling code was not called from within ElapsedTime(), which
made it less frequently called, but that did not seem to be a problem.  And
it was redundant in Curses mode with the FIONREAD call.