Fix proc/pid completion in OS X

[bobthecow]

No description provided.

[ridiculousfish]

I'd love to get these completions working with OS X, but I see a few problems with these changes:

• pgrep is not installed by default on OS X
• __fish_complete_proc doesn't seem to return many processes. (I think you need to pass -x to ps)

Please address these, and I'll be glad to merge.

[bobthecow]

Now that it's the future, both of your concerns should have been resolved. Can we merge it now? :)

[ridiculousfish]

I ended up fixing these a different way. Commit is 6416cb4

[bobthecow]

Sweet :)