add detached process support

* skip detach process support on windows for now
Merge pull request #404 from luvit/features/detached_processes

Feature: Add detached process support
fix filepath
Merge pull request #406 from luvit/fixes/path_windows

fix filepath on windows
Remove warning on used uninitialized variable

The default compilation makes the use of port an error because both
branches of the if have conditions.
Update to latest luajit
Merge pull request #408 from cehoffman/patch-1

Remove warning on used uninitialized variable