doc SA_NOCLDSTOP

[Kevin Ryde]

I added SA_NOCLDSTOP to the sigaction description, and tried to make
it clearer the flags are variables.


     FLAGS is a `logior' (*note Bitwise Operations::) of the following
     (where provided by the system), or `0' for none.

      -- Variable: SA_NOCLDSTOP
          By default, `SIGCHLD' is signalled when a child process stops
          (ie. receives `SIGSTOP'), and when a child process terminates.
          With the `SA_NOCLDSTOP' flag, `SIGCHLD' is only signalled for
          termination, not stopping.

          `SA_NOCLDSTOP' has no effect on signals other than `SIGCHLD'.

      -- Variable: SA_RESTART
          If a signal occurs while in a system call, deliver the signal
          then restart the system call (as opposed to returning an
          `EINTR' error from that call).

          Guile always enables this flag where available, no matter what
          FLAGS are specified.  This avoids spurious error returns in
          low level operations.