Apparently, I have lost the function corner() from the IPT. I have the function cornermetric() I don't do a lot of image processing, but am concerned that I only have partial functionality. This extends to the help where doc corner turns up nothing, whereas doc cornermetric shows the help page
There is no function called "corner" in the image processing toolbox. Therefore I'm relatively sure, that you have not lost it.
From the release notes of 2010b: New corner Function Detects Corners in Image
The new corner function detects corners in a grayscale or binary image. Corners are a feature you can use to find the correspondence between images.
So, I will "accept" Jan's answer since I did not lose it for my version :)