Add Haskell Vim mode

This is a snapshot of the Haskell Vim mode version 20101118 from
http://projects.haskell.org/haskellmode-vim.
Don't try to remove links when they don't exist
Add basic setup for X11 and XMonad
Add the Vim sessions directory
Update .gitignore to ignore XMonad build artifacts
Remove Vim line number support

They ended up being more annoying than useful.