todo

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Implement the event constructors for input operation (inputEvt, ...).

Slow down timer interrupts when pausing for I/O, etc.  When waiting for
just a single kind of thing (e.g., I/O), we can just wait, instead of
sigpause.  Also, we should eventually use asynchronous mechanisms, such
as SIGCHLD and SIGIO.

Add a CML interface to signals.

Add clean-up code for sockets.