NoChdir option

This pull request adds a new `DaemonAttr` option called `NoChdir` that stops godaemon from chdir'ing to / in stage 2.

I've added this functionality because a project I'm working on ([remote_syslog2](https://github.com/papertrail/remote_syslog2)) needs to both daemonize and accept relative paths on the command line. The easiest way to do that is to not `chdir` at all. I don't think there's any downside to this option, I may have missed something?