Fix abspath detection problem in posix
Fix abspath detection problem in posix

Using [github.com/kardianos/osext](github.com/kardianos/osext) solves
the absolute path problem.

Fixes #8
Fixes #10

sevlyar/go-daemon,yookoala/go-daemon,yookoala/go-daemon,lomik/go-daemon,lomik/go-daemon