Fix for incorrect use of shared ptr references
Cleanup of code that decides whether or not to fork. Fix for issue where stderr may be output twice.
Added completions for Vagrant
Portmaster completions

* Added FreeBSD's pkg to __fish_print_packages
* Portmaster completes on installed packages and ports
* Options list as per fish_generate_completions, needs to be tidied
  up further but will suffice for now
Merge branch 'master' into ast
More work on simulating execution of parse trees. Pipes are totally screwed up.
More work on new parser