defer isCanonical computation for getTypeInfo

eb6143234b29c53b2fa9f1978fe02d2b9b46ac96 introduced a patch to fix broken
manage_menu (left pane when using manage).
That fix did not smell good. It was needed because getTypeInfo was computing
isCanonical even though its result is needed only to compute "edit" url.
By deferring the computation of isCanonical to when it is actually needed, the
bad smell can go away.
update changelog