Use knock out of boxen/puppet-knock

Never again. The worst 2 hours of my life, dealing with librarian{,-puppet}
crappy error reporting.
Install HEAD MacVim

See https://code.google.com/p/vim/source/detail?r=37af1e6e91bb1e8ceb89d3ba1c49a04ffd889880
and https://code.google.com/p/vim/source/detail?r=b650f2db8f9604124c0ddfb14af0c04bd4ae0580.
Make lint happy