Update jquery.ckwatermark.js

Further testing highlighted a couple of issues, this new version is more stable.

e.editor.document does not exist if you are viewing the source code so we switch to use e.editor.setData if this is the case.

editor.updateElement tries to keep everything in sync between the editor control, the underlying textarea etc, so this has been added in where appropriate.

The once case that I have not managed to fix up is when you have the text area in focus, you click the source button and then click outside the editor.  This does not fire the blur event for some reason.

If you want to use styles when you are showing your watermark, use a stylesheet style not inline styles as they are reformatted by the editor and the reformatting is different across browsers.