Improve info message in optimize images (fixes #280)
Improve info message in optimize images (fixes #280)

When qpdf can't optimize an image because of an unsupported color
space, state this specifically. Recognize that many valid colorspaces
are not represented as name objects.

qpdf/qpdf,jberkenbilt/qpdf,qpdf/qpdf,qpdf/qpdf,jberkenbilt/qpdf,jberkenbilt/qpdf,qpdf/qpdf,jberkenbilt/qpdf,jberkenbilt/qpdf,qpdf/qpdf