#31 Setting of audiofilepath manually doesn't work

[Sven]

Setting the audiofilepath via entry doesn't work.

[Sven]

Test failed:
- Entering a path with option "Check if path exists" enabled leaves the user a warning after each input. This must be fixed.
- Entering a path crashes with message: "25.12.2012 18:10:36 Version: 0.2.1.35198 | Error in setAudiofilePath of Cuesheet with message: Der Pfad hat ein ungültiges Format."

[Sven]

Problem found:
- The change handler recognizes every change, not the overall change. This needs to be fixed.