* scribble/srcdoc: add `class*-doc` and `class-doc` provide forms.
* Add missing require of racket/class which contains the class? predicate.
* Add @history stanza to class*-doc and class-doc scribblings and bump version number in scribble-lib/info.rkt to 1.30.
One problem involved context that should not be included in
a generated submodule, while another one was an issue with
the previous repair to the shift to label phase.