Fix a few small typos

[guaycuru]

This is my first contribution to this excellent software.
Still a very small one, but I hope to be able to help with more important ones in the future.

[bernardosulzbach]

I would like to see this commits squashed together and merged. It's not offensive to improve the strings this way, it is great.

[ffranco-daitan]

@mafagafogigante @gaubert Commits quashed and rebased. Please merge :)

[bernardosulzbach]

This is better, so it doesn't pollute the history (more than it already is?).

I can't help but add a "please merge" (you know your English, I didn't say that I had commit rights there OK?).

Please merge this, it is a valuable improvement.

[ffranco-daitan]

Yes I know you don't have commit rights, I meant to tell you I did what you asked and ask @gaubert to merge! :D