libc: unix orphan

[bird]

libc is currently killing any processes which are orphaned. The correct behaviour is to convert them to backgroup processes (OS/2 term), i.e. a process which parent is the init process (OS/2 pid 0). This requires either replacing or hooking into the session manager. The first pmshell process is normally serving as the session manager on OS/2, so hooking into it shouldn't be that difficult.