Failing tests showing that removing values for an image CF is broken

Broken by 6a9d0bf.
Process image/file CF uploads from "-Upload" params only

Other CF param actions, such as "-DeleteValuesId", should be processed
normally as they do not contain upload data.  The upload logic was made
too general by the refactoring in 6a9d0bf.

Restrictions on the CF type to Image or Binary still apply since we
don't want to allow arbitrary CF types to store upload data.

This commit makes the newly added t/web/cf_image.t pass.
Merge branch '4.2/removing-image-cf-values'