Add system_info for process_limit and fullsweep_after

Right now spawn does not honour the process_limit
value.
Fix wrong codegen for switch on integer set

Codegen in guards caused call to EObject#unboxToInt 
for objects that are not necessarily integers.
In guard code, we should not fail, but this was
causing a badarg error while evaluating guards.
Fix NIF handling of PIDs and sending
Fix NPE in nif_get_list_cell

If the argument is the empty list, it should
return FALSE, not crash :-)
Fix tcp_inet driver shutdown for multi-accept
Missed commit from system_info fix
Drop support for non-unicode efile ABI