Done some more work this evening on implementing the arbitrary value and other settings for the widget rotation command. All is working well.
What I have noticed however, is that the code for completing the rotation produces a much better quality outcome for large images. I'm not certain why -perhaps it something to do with pixel sampling. I shalln't worry about this too much as who really needs to free rotate really small items anyway? I will explore the use of cairo a little later on, probably when implementing the overwriting of text onto pixbufs.