Merge pull request #495 from hintjens/master

Problem: need local system hostname
Inconsistent Variable Name

The parameter arglist is referenced as args halfway through the
function. Changed the parameter arglist to args.
Fixes for Windows

Windows does not support the %zd argument in printf. Added conditional
compile statement to allow Windows to compile with %u instead of %zd.
Also modified the conditional compile statement for zsys.c so the MSC
and MINGW32 will use _vscprintf.
Merge pull request #496 from danriegsecker/master

Small Modifications
Problem: under some debuggers, asserts in zsys_close

Valgrind, for instance, delays threads randomly at exit, so the
atexit handler can be called while child threads are still alive
and this leads to assert failures in zsys_close when zactor
tries to close its pipe.

Solution: allow zsys_close() after atexit handler has run.
Problem: win32 api calls in portable code

Technique of defining e.g. closesocket to work on POSIX boxes is
kind of horrid; this makes the code harder to copy and understand.
I'd rather be explicit about putting non-portable code into zsys.

Solution: define zsys_udp_close() to close (UDP) sockets.