fix 'moveToEol' behaviour for vim visual block mode

This fixes the `moveToEol` behaviour for visual block mode in Vim. Example of the new behaviour with Ace (which uses CodeMirror's `vim.js` IIUC):

## Before
![vim-before](https://cloud.githubusercontent.com/assets/1976582/5516411/c15eee96-8850-11e4-8617-5ea15e157648.gif)

## After
![vim-after](https://cloud.githubusercontent.com/assets/1976582/5516412/c422966e-8850-11e4-894a-feb4ed76dca2.gif)