Ensure yanked text ends with newline if motion is line-wise

Add newline character to the register when the yanked line is the last line of the document and the motion is linewise.

Fixes the following situation:

- Yank a whole line `yy` at the last line of the document (**no newline after it**).
![a1](https://cloud.githubusercontent.com/assets/4009153/3683738/9f6a40ee-12ec-11e4-8f01-ee2cc2281fc1.png)

- Paste with count: `3p`
![a2](https://cloud.githubusercontent.com/assets/4009153/3683739/a2eddd16-12ec-11e4-9464-a89eb6237b44.png)

It should paste whole lines:
![a3](https://cloud.githubusercontent.com/assets/4009153/3683759/16bc324c-12ed-11e4-96c7-e0ce2d8a25d3.png)

It only happens when the yanked line has no line after it.

I've fixed it in the `yank` operation, ensuring that, the copied text has a '\n' at the end if the motion is line-wise.