wait for the end of a particular child process.
int mbkwaitpid( pid, mode, status )
Process number to wait.
If mode is set to 1, this function return only when the child process is
terminated. Otherwise, function return immediatly.
If not NULL, the exit status of terminated child process.
mbkwaitpid provides a centralized way to catch terminated child process.
Because some Alliance library can create a child process, and user application
can do so, there must be a centralized way to get the exit status of process.
The programmer should never modify the handler for SIGCHLD.
mbkwaitpid return 1 if child process is terminated, and 0 if isn't (case
mode != 1 ).