SMP and kernel poll

[Christophe Romain]

I tryed to patch  erts/emulator/sys/unix/sys.c without any success. I 
always got file descriptors mess while calling devpoll_update_pix (get 
a fstat error).

this module needs a rewrite and in the current state does not seems to 
allow kernel poll and smp. I rewrote a little bit this module to make 
it more readable (suppress some #ifdef, using function pointers) and 
got the same error.