[vtkusers] rotate image - user interaction

[Matthias Zangl]

Hello!

I created a slice-viewer. Slicing through the images is no problem at all.
Its also possible to rotate the image after loading. But I want the user to
control the rotation of the image with buttons.
This won't be a problem if I could reset the previous rotations before doing
the next rotation.

1. I read the images with a reader
2. I assign the reader-output to a pointer
3. I assign the pointer to imagereslice.
4. I do the rotation
5. I do the rendering stuff

Well, the first time works great. The second time I am starting with step 3
because I believed that there should be the unmodified reader-output. But it
has already been modified.

I think I am violating against the pipeline-concept. Maybe there's a better
way for doing this.

Any suggestions to point me to the right direction would greatly be
appreciated!!!

Kindly regards,
Matthias