forkProcess type changed?

[George Russell]

For the development snapshot 6.3.20031201, System.Posix.forkProcess
has the type IO () -> IO System.Posix.Types.ProcessID.  In 6.0.1
it has type IO () -> IO (Maybe System.Posix.Types.ProcessID).  Is
this change intentional, and if so how are you supposed to test
after the fork if this is the parent or child process?