net/http-client: restore use of `abandon`

The difference between `abandon` and `close-output-port` seems to
matter for downloading PLaneT packages on some networks. Using
`abandon` does not seem to create any problems now that an extra
"\r\n" is not incorrecty included in PUT/POST requests.
scribble: document all `scribble/manual` CSS style classes

Includes a few Scrible bug and documentation repairs.
racket/gui win32: fix for backing-scale

Closes PR 14278