Changes include
- the undo cursor and undo selection are saved with the first KateDocument::editStart()
- the redo cursor and redo selection are saved with the last KateDocument::editEnd()

For this to work, the following parts needed to be fixed
- wrap doDeleteWordLeft/Right with editStart() and editEnd(), otherwise wordLeft() and wordRight() change the cursor position
- drag & drop: while moving the cursor position is changed. To make it work, we need to fix the cursor position before we really do the drop operation. The undo selection is only set in the case of a move, otherwise it does not make sense (it feels really strange)

Please test the patch, as it should go into KDE 4.1 if it works. Right now, the KDE 4.1 branch crashes sometimes when doing undo/redo.

Port to KDE 4.1.0? Wait for KDE 4.1.1? dunno...