Implement command builtin about oil

[andychu]

OK so you use this command interactively? I tend to use which clear instead, but we should have the bash version too.

[timetoplatypus]

which is from the GNU project I believe, so it may not always be on the system. command is more generally a UNIX/POSIX builtin convention, and I think if OSH wants to be a UNIX shell it should include this.

[andychu]

Yeah I was saying we should have it. But I didn't know it was in POSIX:

http://pubs.opengroup.org/onlinepubs/9699919799/utilities/command.html

And this thread says which is not in POSIX: https://stackoverflow.com/questions/762631/find-out-if-a-command-exists-on-posix-system

[timetoplatypus]

Yup, command is quite useful and it's common to see in shell scripts in general (not just bash scripts)

[andychu]

OK, this is done for -v now. Let me know if you run into problems.

[timetoplatypus]

Just updated my OSH install to include the latest commits. I can verify that the command builtin is functioning with the -v flag.

[andychu]

Fix released with 0.3.