Disable Syntastic's automatic syntax checking for Haskell

Because the error messages are not wrapped.
Instead, use C-c C-c to do manual checks (use ghcmod-vim).
Map C-c C-t to :GhcModType in Haskell buffers
Map C-x and C-c only in Visual mode
`au BufEnter {*.x,*.y} setl ft=haskell` for syntax highlighting