Reversed sides of original and replacement in file conflict dialog

Fixes #5444 

Now the dialog looks like this:
![fileconflict1](https://f.cloud.github.com/assets/277525/1375497/39834006-3a83-11e3-914b-0a8536eddfd3.png)

Please review @karlitschek @jancborchardt @butonic @Kondou-ger